The 92-year-old queen and her husband Philip, 97, who has retired from official engagements, were joined by other royals and celebrities including Hollywood stars Liv Tyler and Demi Moore, models Kate Moss and Naomi Campbell, and singers Ellie Goulding and Robbie Williams.
United Kingdom star Robbie Williams gave a surprise performance at Princess Eugenie's wedding, a guest told Page Six, as supermodels and stars boogied.
The princess also wore a attractive tiara made of emeralds and diamonds pavé-set in platinum, which was originally owned by the Queen Mother and lent to her by Queen Elizabeth II.
Eugenie set off her evening look with diamond and emerald drop earrings which were a wedding gift from the groom, and a hair slide belonging to the Queen. It looks like Meghan and Harry's touchy-feely vibes were contagious, because Prince William and Kate Middleton (who were sitting next to them) also had a rare PDA moment: They were photographed holding hands in the pews.
Although the day was a tad windy, guests made it through with a few lost hats and a handful of dress clutches (à la Marilyn Monroe).
Wearing a maroon dress, the famed actress attended the event, as she is friends with Eugenie's parents.
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The dress features a fitted off-the-shoulder bodice with low back and full skirt draping beautifully into a flowing full length train behind her.
Princess Eugenie and Jack Brooksbank leave the church after their wedding ceremony.
These viewing figures are significantly down on the Duke and Duchess of Sussex's wedding which saw a peak audience of 18 million. She was led down the aisle by her father, Prince Andrew.
Eugenie, 28, works at a contemporary art gallery.