Life is full of milestone birthdays worth a big celebration, but turning 21 marks the start of adulthood.
So, it's no surprise that Carole and Michael Middleton pulled out all the stops to mark the occasion for their eldest daughter Kate.
Six months after her actual birthday, in June 2003, they organised a big 1920s themed party and sit-down dinner for Kate's closest friends and family, including her new secret boyfriend Prince William.