Happy birthday to Prince William! The heir to the throne turns 44 on June 21 - coinciding with Father's Day in the UK - and is expected to spend the occasion privately with his wife Princess Kate , and their three children: George , Charlotte , and Louis . As one of the most famous people on the planet, and a key figure in theR Royal Family , the prince is a permanent fixture in the public eye, anchoring everything from grand state occasions like Trooping the Colour to low-key charity visits.