Harper Beckham and her friends pose with Princess Eugenie. Photo / David Beckham Instagram
David Beckham has been forced to deny Buckingham Palace was hired out as a venue for his daughter's birthday party after pictures of a private function organised by the Duchess of York sparked a royal row.
Harper, David and Victoria's youngest child, attended a tea party last week with Princess Eugenie and a host of school friends just days before her birthday, with the pictures - including the youngster holding a balloon - being uploaded today, the day she turned 6.
However, after an unprecedented move experts have warned the palace should not be a "party venue for millionaires" and the Beckhams soon faced calls that they had been given hugely preferential treatment, the Daily Mail reports.
Alongside a picture of himself, his mother and Harper, he wrote: "One last picture of the birthday girl.... Just to be clear this wasn't the palace opening the gates for Harper's birthday party , this was a tea party where us and other guests were invited so it was a beautiful thing to do with My mum , Harper plus a few school friends... We were honored to be able to there... Beautiful tea party...."
But royal expert Robert Jobson told MailOnline he had never heard of such an offer being extended to non-family members before.
"It seems odd to me that if you have the money or connections, the Palace - a building funded by the British taxpayer - can be used in this way for a selected few.
"The palace is undergoing a huge renovation in the coming years at a cost of multi millions to the British taxpayer. If this is a new policy to make money it should be clear and open to everyone.
"If it is just for the rich and famous it is simply not right. The palace is used by the Queen and members of the royal family to host receptions to promote the national interest, for diplomacy or say to thanks our sporting heroes, such as our great Olympians.
"It is not a party venue to be hired out to millionaires because they have a friend once connected to the royals."
Jobson, who broke the news of Charles and Camilla's wedding and has written books such as The Future Royal Family, confirmed that private functions of any sort in the palace were not common - and never happened for birthdays - also saying he was "surprised" the Duchess of York had such pulling power.
"The palace officials, when selling the huge cost to the taxpayer of the palace refurbishment talked of appealing to people's 'sense of nationhood'.
"The palace is the venue for glittering state occasions but when it is used - or misused -like this, surely the public is entitled to know how it came about, who organised it, was money paid and why it is only open to rich and famous ex footballers."
A Buckingham Palace spokesman said: "From time to time members of the Royal Family who reside at royal residences invite guests to visit privately."
The Mail understands that Prince Andrew was present at the time, although he does not appear in any of the social media postings.
A royal source added: "Any costs were covered privately."
A spokesman for the Beckhams later reiterated that they had been invited as guests of Sarah Ferguson, despite the Duchess of York not being present in any of the photos, and that the event had nothing to do with Harper's milestone.
They told MailOnline: "Let me be very clear this was a private tea party last week that the Duchess of York organised."
The Duchess of York is no stranger to controversy, after she was secretly filmed offering to sell access to Prince Andrew for Β£500,000 ($885,000).
A News of the World video in 2010 showed Sarah Ferguson promising to introduce an undercover reporter posing as a wealthy businessman to the Prince, who has been the UK's special representative for international trade and investment since 2001.
During a covert film of the agreement, the Duchess was apparently handed a US$40,000 ($55,000) cash down payment.
She was filmed telling him how to transfer Β£500,000 to her UK bank account and said: "Then that, is then like, then you open up all the channels whatever you need, whatever you want, and then that's what and then you meet Andrew and that's fine. And that's, that's when you really open up whatever you want."
The paper said that, despite the Prince knowing nothing about the deal, the Duchess claimed to have discussed it with him: "Andrew said to me, 'Tell him Β£500,000'.
"He knows that he's had to underwrite me up to now because I've got no money. So if you want to meet him in your business, look after me and he'll look after you. You'll get it back tenfold."
The Duchess later said she was "devastated" and "regretful" about the incident.
Instagram was awash with critics who were less than happy about the photos, with one writing: "If you have enough money you can anything!!"
Another said: "Is this a new commercial venture by the Royal family or do all little princesses now get an invite?"
Another simply posted "Cash".
Harper was invited with her friends to attend the party inside a small drawing room and also stood in the grounds of the palace holding a balloon for one snap.
She wore a blue fairytale gown to mimic Elsa from Frozen for the special day.
Victoria Beckham shared the image without alluding to the unexpected location of the tea party, writing: "Our little birthday princess x Kisses."
Once inside, she posed with her friends and Princess Eugenie, and David Beckham posted the snap to Instagram.
He wrote: "Lucky Harper, meeting a real-life princess at the Palace," alongside a kiss and heart emoji.
Harper's brother Cruz, 12, wrote: "Dear Harper I can't believe it has been already 6 years yoyo are such a big girl so to the best sister in the world I love you so much have a amazing day."
Her eldest brother Brooklyn, 18, shared this sweet snap, writing: "Happy birthday to my little sister. Love you so much."
Romeo, 14, shared another sweet snap, writing: "Happy birthday to the best sister in the world!!!!!! I hope you have an amazing day. I love you so much."
David Beckham shared another snap of himself cuddling his daughter, who was wearing a cream lace dress.
He wrote: "Happy Birthday to our special little young lady ...Such a special girl who brings so much joy and happiness into our lives.. Happy 6th birthday."
"( I can't believe your 6 already ) have the most amazing day we love you pretty lady x @brooklynbeckham @romeobeckham @cruzbeckham @victoriabeckham."
And the family's fans went wild for the snaps and took to the comments section to wish the youngster well.
They wrote: "She is a real princess. Happy birthday Harper."
Another said: "This would have made my life at age 6 there would have been no up for me from this!!!"
A third wrote: "Happy birthday princess always the the best."
Another wrote after David Beckham's final post: "You shouldn't feel that you have to explain yourself David! Love the pics, truly special and memorable afternoon. Happy Birthday to Harper!"
A second subsequent post read: "Beautiful but why on earth are you justifying where/what/why ..... enjoy whatever moments you can in life."
It's not the first time the Beckhams have been at the palace.
Victoria Beckham received an OBE for her contribution to fashion from the Duke of Cambridge in April.
The Spice Girl turned fashion designer, received the award more than 13 years after her husband, former England captain David Beckham, was granted the same title for his services to football.
The 43-year-old said afterwards: "It was an absolute pleasure to be at Buckingham Palace today. I'm proud to be British, honoured and humbled to receive my OBE from the Duke of Cambridge.
"If you dream big and work hard you can accomplish great things. I'm so happy to share this very special occasion with my parents and husband; without their love and support, none of this would be possible."
Victoria Beckham was not accompanied by her four children on the day, but Romeo shared a sweet message for his mother on Instagram.
"Mum, I love u so much and hope you have the best day ever!! You are the most amazing mum and you are perfect In every way. I love how you make me laugh every day and whatever happens you always seem to be happy. I love you to the moon and back xx have the best day ever !!" the teen wrote.
Sources close to the family told MailOnline before Christmas that Victoria, 42, was "delighted and humbled for the recognition".
Victoria's husband-of-17-years David received his OBE at Buckingham Palace in 2003 for services to football, his wife by his side.
Speaking last year for the documentary Our Queen At Ninety, the former sportsman said it remained one of his proudest moment.
"That day was special for me because I brought my grandparents with me, it made me proud that I could bring them to somewhere that they worshipped for their whole lives."
He added: "Meeting the Queen, it doesn't get better than that. You can feel the emotion, I can personally feel the emotion, because I just love everything about our Queen and what she represents.
"We all look for role models, we all look for leaders. I'm privileged and proud that we have the number one leader."
Despite his gushing comments, David Beckham became embroiled in an email hacking scandal in February, surrounding his honour.
Leaked emails suggested Beckham hoped his Unicef campaign would help win him a knighthood. However, when he failed to receive one, he branded members of the honours committee "unappreciative c****".
The former England captain dismissed lower awards, ranting: "Unless it's a knighthood f*** off".
According to the revelations, the Honours Committee had already agreed that Beckham's nomination - almost certainly proposed by his PR advisers - was well "merited" before a routine check of his tax affairs.
Meanwhile, in an interview with Esquire magazine in 2012, Beckham said he counted Princes William and Harry as friends.
He said at the time: "Yeah, I think I would, [call them friends.] It's a very normal relationship. With Harry as well. They're very easy to get along with. They love their sport.
"William loves Aston Villa, unfortunately, which obviously I give him a bit of stick about."