Meghan Markle said "yes" immediately to Prince Harry as he got down on one knee to propose, the couple revealed in their first interview after their engagement was announced.
Prince Harry popped the question while the couple were having a "cosy night" in Nottingham Cottage, the Prince's home at Kensington Palace, roasting chicken.
Markle revealed the moment was "so sweet and natural and very romantic" and Prince Harry couldn't finish his sentence before she said yes.
The engagement was announced by the Prince of Wales on Monday morning in the UK with a statement saying the couple, who have been dating for 16 months, will marry in the northern spring next year.
The couple spoke to BBC presenter Mishal Husain in their first interview since the announcement and revealed that they met when they were set up by a female friend.
"It was definitely a set up - it was a blind date," Markle said.
After their first date they organised to see each other the following day, and Harry said he knew Markle was "the one" immediately.
"When did I know she was the one? Very first time we met," the Prince said.
Four weeks after they met, Harry persuaded Markle to join him on a five-day break in Botswana.
"We camped out with each other under the stars, we spent - she came and joined me for five days out there, which was absolutely fantastic," he told Husain.
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 appeared at a photo call at the sunken gardens, Kensington Palace, and answered a number of questions from the waiting press.
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.
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.
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.
"To see her union with Harry, who shares the same qualities, is a source of great joy for us as parents.
"We wish them a lifetime of happiness and are very excited for their future together."