The Queen gave Prince William permission to use her 900-year-old royal fortress, the Windsor Castle, for a gala dinner to celebrate the work of The Royal Marsden, one of Princess Diana's favourite hospitals.
The Duke of Cambridge did not hold back and put together a guestlist that was star stuuded and fit for the future King of England. The high profile list included Kate Moss, Helena Bonham Carter, Cate Blanchett, Benedict Cumberbatch, "Harry Potter" actress Emma Watson, celebrity photographer Mario Testino and "Downton Abbey's" Laura Carmichael.
No matter how star studded the list was however, Britain's biggest fashion icon, his wife, the Duchess of Cambridge, was left at home tending the baby and was notably absent from the affair.
Her decision to stay in with 10-month-old Prince George was part of the couple's strategy, begun a few months ago, of maintaining a focus on their own individual charity patronages and dividing their duties so they can be present at more events.
As the Queen and Prince Philip slow down, royal aides have let it be known that other members of the Royal Family will be using Buckingham Palace, Windsor and other royal residences increasingly to host official events.
William became president of the Royal Marsden in 2007 and is quite keen on adopting his late mother's legacy.
Big time fashion designer Ralph Lauren, was also at the event and announced that he is funding an entire new breast cancer centre at the London hospital. Mr Lauren, 74, and his wife Ricky, flew from the United States to attend the event and launch the Ralph Lauren Breast Cancer Centre.
Lauren, who had a benign brain tumour removed 25 years ago and lost his close friend Nina Hyde to breast cancer in 1990, has donated millions to cancer research around the world in the past 20 years. William was quick to admit that the Laurens would have probably been more pleased to see his wife Kate, who is the fashion icon in the family
The fashion designer, who has built up a £4 billion fortune, said he was excited about meeting the Duke for the first time, having known William's mother through their common interest in fighting cancer.
"He's taken up his mother's movement; Tonight's not a fashion moment as far as I'm concerned; it's a moment of connection." Mr Lauren said about William.ore a thigh split dress [PA]
"Everyone loves her in the US. She's got a charming way about her and she's very beautiful. I think she's doing her job - as the Prince's wife and mother of the future King - perfectly," he remarked when asked about Kate.
In tribute to his generosity, the stars all wore Ralph Lauren from head to toe at the dinner.
Lauren Bush, niece of former US President George W Bush, sported an embroidered bustier and cream jersey skirt; Blanchett an ivory silk cady evening dress with Ralph Lauren watch, jewellery, and diamond chandelier earrings.
Emma Watson wore a Ralph Lauren Collection silk jersey evening skirt and shirt; Helena Bonham Carter was in a midnight navy silk taffeta and organza evening dress, while even Cumberbatch wore a Ralph Lauren tuxedo.
The Royal Marsden is the oldest, largest and most comprehensive cancer centre in Europe, with a history of ground-breaking research. William has immersed himself in the work of the hospital.
He also supports the work of the Royal Marsden Cancer Charity, a member of the Charities Forum overseen by the Duke and Duchess of Cambridge and Prince Harry as joint patrons.
Officially, the dinner was being held "to celebrate the innovative work of The Royal Marsden and bring together the Hospital's world-leading consultants, supporters and philanthropists".