Prince Harry has said he knew his bride-to-be Meghan Markle was "the one" from the moment they met, as the couple made their first public appearance since the announcement of their engagement.
The Prince, 33, declared that he is "thrilled" as he and the 36-year-old American actress posed for an open-air photocall in the Sunken Garden at Kensington Palace.
Their long-anticipated engagement was announced by the Prince of Wales on Monday morning with a statement saying the couple, who have been dating for 16 months, will marry in the northern spring next year.
A beaming Markle, in a white belted coat, clutched Harry's hand with both of her hands as they posed briefly and showed off her diamond engagement ring - designed by the prince.
Harry revealed that he knew Markle was "the one" from the first moment they met. "When did I know she was the one? Very first time we met," the prince said.
The couple will this afternoon be interviewed by the BBC's Mishal Husain for a programme that will be screened at 6pm.
Speaking in the Sunken Garden, Markle said she was "so very happy, thank you" to be engaged to Harry.
The prince said he was "thrilled, over the moon" adding: "Very glad it's not raining as well."
The couple were smiling and giggling throughout their appearance.
When Harry was asked how he proposed, Markle replied "Save that", and Harry added: "That will come later".
Kensington Palace said the prince designed Markle's engagement ring - using two stones that belonged to his late mother.
The two outside stones are diamonds from the personal collection of Diana, Princess of Wales.
At the centre is a diamond from Botswana, a country that holds special significance for Harry, who has visited many times since he was a child.
It is also a place the couple have spent time together over the past year and a half, Kensington Palace said.
The band is made of gold and the ring was made by Cleave and Company, Court Jewellers and Medallists to Her Majesty The Queen.
The couple braved the cold and answered a number of questions from the waiting press, before waving at the cameras and walking back through the garden arm in arm.
The sunken garden is poignantly the site of the memorial garden created this year in memory of Diana, Princess of Wales to mark the 20th anniversary of her death.
It was one of the princess' favourite parts of the palace grounds.
— The Duke and Duchess of Cambridge (@KensingtonRoyal) November 27, 2017
Harry and Markle were separated from the media by several metres of water, standing on the other side of the large ornamental pond.
Markle's white coat was by Canadian brand Line the Label, and her dress by P.A.R.O.S.H.
It appeared as if the Meghan Effect was already under way, as Line the Label's website crashed because of the numbers of people trying to access it.
Markle's shoes appeared to be strappy Aquazzura Matilde Crisscross Nude Suede Pumps.
Earlier, the Queen and Duke of Edinburgh said they were "delighted" for their grandson and his bride-to-be, and "wish them every happiness".
The Duke and Duchess of Cambridge said: "We are very excited for Harry and Meghan. It has been wonderful getting to know Meghan and to see how happy she and Harry are together."
Markle's parents wished their daughter and Harry "a lifetime of happiness", adding: "We are incredibly happy for Meghan and Harry.
"Our daughter has always been a kind and loving person. To see her union with Harry, who shares the same qualities, is a source of great joy for us as parents."
Visiting Poundbury in Dorset on Monday, the Prince of Wales said he was "thrilled" and "very happy indeed" for Prince Harry and Markle.
Fifth in line to the throne, Harry has been dating Markle - who found fame in the US legal drama Suits - since summer last year.
Their 16-month whirlwind romance blossomed when they met through mutual friends in London, and the pair have been almost inseparable in recent months.
The much-anticipated news was confirmed by the Prince of Wales in a brief statement issued by Clarence House.
The Prince of Wales is delighted to announce the engagement of Prince Harry to Ms. Meghan Markle. pic.twitter.com/zdaHR4mcY6
— The Prince of Wales and The Duchess of Cornwall (@ClarenceHouse) November 27, 2017
It read: "His Royal Highness the Prince of Wales is delighted to announce the engagement of Prince Harry to Ms Meghan Markle."
It revealed that the pair became engaged in London this month.
"Prince Harry has informed Her Majesty the Queen and other close members of his family. Prince Harry has also sought and received the blessing of Ms Markle's parents," the statement said.
The couple will live together in Harry's current home, Nottingham Cottage at Kensington Palace.
Markle will become an HRH and a senior royal after marrying Harry and joining the Windsors.
She is expected to become a duchess - just like Kate Middleton did when she became the Duchess of Cambridge after saying her vows in 2011.
But unlike Kate, Markle is not a future queen. With the arrival of the Cambridges' children, Harry is too far down the line of succession to have a realistic prospect of being monarch.
Markle will most probably become HRH the Duchess of Sussex, if Harry is made the Duke of Sussex by the Queen on the morning of his wedding.
The pair were secretly engaged this month and rumours a wedding was imminent stepped up a gear when Harry took Markle to meet his grandmother the Queen for tea at Buckingham Palace.
The Queen has given her blessing to the union. Prince Harry, as fifth-in-line to the throne, is obliged to ask her permission under the Succession to the Crown Act 2013.
Markle has been wed before, marrying film producer Trevor Engelson in Jamaica in 2011, but splitting after just two years.
Meghan Markle's parents tell of 'great joy'
In a statement issued by Kensington Palace, Markle's parents Thomas Markle and Doria Ragland said: "We are incredibly happy for Meghan and Harry. Our daughter has always been a kind and loving person.
The world reacted with joy to the long-awaited news that Prince Harry is set to marry Markle.
Theresa May
Prime Minister Theresa May offered her "very warmest congratulations", wishing the couple "great happiness for the future".
"I would like to offer my very warmest congratulations to HRH Prince Harry and Meghan Markle upon their engagement," said May.
"This is a time of huge celebration and excitement for two people in love and, on behalf of myself, the Government and the country, I wish them great happiness for the future."
I would like to offer my very warmest congratulations to HRH Prince Harry and Meghan Markle upon their engagement.
This is a time of huge celebration for two people in love and, on behalf of myself, the Government and the country, I wish them great happiness for the future. https://t.co/Sfx76X98BW
Justin Welby, the Archbishop of Canterbury, said he was "absolutely delighted to hear the news", wishing them "many years of love, happiness and fulfilment".
I’m absolutely delighted to hear the news that Prince Harry and Meghan Markle are now engaged. I wish them many years of love, happiness and fulfilment – and ask that God blesses them throughout their married life together.
The Israeli President, Reuven Rivlin, was the first world leader to publicly send his congratulations - going as far as to invite the happy couple to honeymoon in Israel.
Mazal Tov to HRH Prince Harry & fiancé @MeghanMarkle. Sending our warmest regards to Her Majesty the Queen, Duke of Edinburgh, all the Royal Family & the British people, from Nechama & me, & all the Israeli people. We invite them to enjoy their honeymoon in Israel!
Tessy Ojo, chief executive of the Diana Award, said: "The Diana Award offers their warmest congratulations to Prince Harry and Meghan Markle on their engagement and we wish them every happiness for the future.
"Prince Harry has had a huge impact on the young people he's met through our youth charity set up in memory of his mother Princess Diana. We know how delighted our young people will be to hear this news today."
Absolutely delighted for Prince Harry and Meghan Markle.
But Corbyn said: "My congratulations to Harry and Meghan. I wish them well. I hope they have a great time and great fun together and having met Harry a couple of times I'm sure they're going to have a great deal of fun together.
"I really do admire the way Harry and his brother are actually drawing attention to mental health conditions all across the country.
"So I wish him well, thank him for what he's done on mental health, and I hope they have a great life together."
Royalists full of excitement after announcement
Tourists and royalists gathered outside London's royal residences spoke of their excitement at the news of the engagement.
Royalist town crier, Tony Appleton - who was outside Buckingham Palace ready for the announcement, said he had arrived in the capital at 7am on Monday because he expected the news.
"I had a premonition last night," the 81-year-old from Great Baddow, Essex, said.
Quizzed on what the engagement announcement means to him, he said: "Everybody wants Harry to get married, including me. I think this seals it, absolutely. I think if Diana was alive she would be so proud of him, so proud of him."
He said he will be there for the latest royal wedding, ringing his bell to congratulate the couple.
Dressed in a bespoke town crier uniform worth more than £5500 ($10,600), he said this is the biggest announcement he has made since the births of Prince George and Princess Charlotte.
"It has broken a bit of tradition what he has done, but I think it is absolutely fantastic," he added.
Outside Kensington Palace, American tourist Laurie Mallen, who is visiting from Boston with her parents, said: "The transatlantic friendship's always been there, but I think this is just going to further that and really cement that.
"She's a great representative of America. She's a professional person, with all the charity work she's done, she has a huge personal interest in doing good, that's what she'll be able to bring, and will probably be able to expand upon by being part of the royal family."
Mallen said she has been receiving text messages from her American friends asking if she had heard the news.
"I'm sure there will be some wedding-watching parties," she said. "Will and Kate's wedding was huge, there were tonnes of people getting together at four in the morning to have tea parties."
Tourist Daniel Belet, 71, from France - who was at Kensington Palace as he visited the city with his wife, said they were excited about the engagement, and admitted they enjoy the royal family.
Agreeing there is a "fascination" in France with the British royals, he joked: "We cut the head off Louis, but we are very fond of foreign royalties."
'Cinderellas are crying': World-wide media reaction
Russia: Harry has 'broken those hearts once and for all'
"Cinderellas are crying: Bachelor Prince Harry has announced his engagement," read the headline on the site of the popular Russian newspaper Moskovsky Komsomolets, reports Alec Luhn.
"The youngest nephew of Queen Elizabeth, who has for many years been stirring up the hearts of girls around the world, has broken those hearts once and for all," the paper wrote.
Although Prince Harry is "one of the most envied bachelors on the planet", he "has not until now demonstrated any inclination toward monogamy", it added, explaining that paparazzi had often photographed him "at wild parties with one beauty or another".
"Prince Harry and Meghan Markle have announced their engagement. Clear out, girls," tweeted TV Rain.
Italy: 'A revolution for the British royal family'
"The long-awaited announcement has arrived," says Corriere della Sera, one of Italy's leading papers, on its website, reports Nick Squires. "Harry and Meghan will marry in the spring."
The paper comments: "The announcement of the engagement signals a revolution for the British royal family. After William's marriage to the 'commoner' Kate Middleton, Her Majesty Elizabeth II has given her blessing to another 'unusual' union for Buckingham Palace, with the arrival in the royal household of an American divorcee with a black mother."
France: Meghan is 'a Kate Middleton a l'americaine'
Madame Figaro called the royal bride-to-be "a Kate Middleton a l'americaine", reports Henry Samuel.
In a long online piece, the magazine writes: "The American actress and Prince Harry had waited 15 months to make their relationship public. A blessed period for the future Princess of Wales who loved keeping these moments 'just for them'."
"[This quiet period of] happiness would prove to be short-lived as on 23 September 2017, the duo unleashed passions by appearing hand in hand at the Invictus Games in Toronto. A documentary, an incendiary book by her half-sister, interviews and hundreds of articles later, she who came to celebrity late has seen her innermost secrets splashed across the media of the world."
"At last!," headlined RTL radio in an online piece. "Her Majesty's subjects could bear the wait no longer. The British had already fallen head over heels in love with William and his bride Kate Middleton.
"Their wedding, the long white dress of a then mere commoner, the kiss on the balcony of Buckingham Palace... such images remain engraved in the kingdom's collective conscience. Now, the United Kingdom will have a second memorable ceremony."
"His Royal Highness The Prince of Wales is delighted to announce the engagement of Prince Harry to Ms. Meghan Markle.
"The wedding will take place in Spring 2018. Further details about the wedding day will be announced in due course.
"His Royal Highness and Ms. Markle became engaged in London earlier this month. Prince Harry has informed Her Majesty The Queen and other close members of his family.
"Prince Harry has also sought and received the blessing of Ms Markle's parents.
"The couple will live in Nottingham Cottage at Kensington Palace."
Where will the royal couple live?
Prince Harry and Markle are to move into Nottingham Cottage, a snug, two-bedroomed property in the grounds of Kensington Palace.
The cottage was previously occupied by the Duke and Duchess of Cambridge, who used it as their London base for around two-and-a-half years.
Just a stone's throw from Kensington Palace, Prince Harry's childhood home, the cosy property, known by royal insiders as "Nott Cott", boasts two bedrooms, two reception rooms, a bathroom and a small garden.
The ceilings are said to be so low, the Duke of Cambridge had to "stoop" to avoid banging his head on them.
An ideal starter home for newlyweds, the property also provides fantastic access to the trendy shops, boutiques and spas on Kensington High Street with which Markle is already familiar.
Having stayed with Prince Harry, 33, at the private, self-contained cottage whenever she has flown from Toronto to visit him, she will already feel very much at home there.
Nottingham Cottage is one of the smallest properties within the grounds of Kensington Palace and was formerly the home of the Duke of Edinburgh's private secretary, Brigadier Sir Miles Hunt-Davis, and his wife Gay.
Princess Diana's sister Lady Jane Fellowes and her husband Sir Robert Fellowes also lived there.
How anticipation built for announcement
Her engagement to Prince Harry has been hotly anticipated by royal watchers, after the couple made their first public appearance together hand-in-hand at the Invictus Games.
Walking hand-in-hand, they watched the wheelchair tennis together in an affectionate half an hour together in front of the world's media.
Markle had also made an appearance at the Games' opening ceremony, sitting apart from Prince Harry but under the watchful eye of his protection officer.
Speculation had already been building after an extraordinary interview with Vanity Fair in which Markle declared the couple were "in love".
Until then, they had managed to keep details of their early romance largely under wraps, after being introduced by mutual friends in London in July 2016.
In October 2016, their fledgling relationship was exposed in a Sunday newspaper, and confirmed a week later in an unusual statement issued by Prince Harry pleading for Markle to be given her privacy.
Over the following months, they were photographed together on several occasions including visiting the theatre in London and at a friend's wedding in Jamaica.
While Markle worked on Netflix drama Suits in Toronto, Canada, she and Prince Harry flew back and forth regularly as their relationship deepened.
In May 2017, the pair were photographed embracing at a polo match in Ascot, with Markle spending time with new friends including Mark Dyer, a former Army officer often described as Prince Harry's mentor.
Later that month, the actress attended the wedding reception of the Duchess of Cambridge's sister, Pippa Middleton, who wed James Matthews in a no-expenses-spared day for their rich and famous friends.
The summer of 2017 saw the Prince, 33, whisk Markle to Botswana and Zambia for a romantic holiday, with reported outings on safari and to Victoria Falls.
By the time she gave an interview to Vanity Fair, the engagement seemed all but a formality. In an unexpectedly frank article, conducted with the blessing of Prince Harry, the actress confirmed: "We're a couple. We're in love."
Calling him her "boyfriend" publicly for the first time, she said: "We're two people who are really happy and in love." The actress said they were treasuring "our time", before sharing details of their relationship with the watching world.
She has already begun the transformation to royal life, shutting down her lifestyle blog and rumoured to be leaving legal drama Suits at the end of its next season.
Kate Middleton also gave up her job as an accessories buyer for Jigsaw ahead of her engagement to Prince William in 2010.
The Prince has made no secret of his ambition to settle down. In 2015 he spoke of hoping to find someone to be "next to him" and share the unusual pressures of royal life.