Prince William and Kate Middleton joined Prince Harry and Princess Beatrice as guests at the marriage of friends Harry Aubrey-Fletcher and Louise Stourton, at St Andrews's Church in Aldborough, near Harrogate.
Miss Middleton, who walked separately into the church, accompanied by a police protection officer, wore a black dress and hat to the service, while Prince William, who was an usher, joined friends at a local pub before the service. After the service, a vintage double-decker bus transported the wedding party from the church to the reception at Allerton Park.
Yesterday the royal bride-to-be celebrated her 29th birthday, her last as a commoner.
It is not known what Prince William has in mind as a present for his betrothed but it is likely Miss Middleton would be keen to take extra care, following reports the pearl earrings he bought last year were eaten by Miss Middleton's pet cocker spaniel, Otto.
The dog apparently took them from an ornamental dish at the side of her bed and left its tooth marks behind in a tube of handcream.
A patient wait for nature to take its course was required before the antique jewellery resurfaced.
While the younger Royals were enjoying the birthday celebrations, the Queen and Duke of Edinburgh yesterday attended a church service amid tight security.
About 150 members of the public gathered outside St Mary Magdalene church on the Queen's estate at Sandringham, Norfolk, to watch the royals arrive and leave.
The royal couple listened to a sermon by visiting preacher Barry Morgan, the Archbishop of Wales.
After the service the Queen accepted flowers and gifts from about a dozen children.
The Queen and Duke traditionally spend Christmas and the New Year at Sandringham.