Happy birthday, Prince William!

Britain's second-in-line to the throne turns 31 today, just a few weeks before the birth of his son or daughter. Kate is officially on maternity leave, but we're sure she'll be celebrating with her husband.

The elder son of Prince Charles and the late Diana, Princess of Wales, William is next in line to the throne following his father. He was born on June 21, 1982, and received a brother just a few years later. Educated at four schools in the UK, he was fifteen years old when his mother passed away. He went on to attend St. Andrews University, where he would meet Kate Middleton, now his wife.

Just before he and Kate were wed on April 29, 2011, William was given the title Duke of Cambridge by the Queen. Ever since the boys were young, they had a passion for many causes -- instilled in them by their mother, Diana. William has honored her legacy by his involvement in organizations that combat disease, homelessness, children's issues and environmental problems.

Happy birthday to the Duke of Cambridge, and we know he's anxiously awaiting the best gift of all, his heir. Click through the gallery to see his style transformation!

On a more serious note, what do you think? Will the royal heir be a Prince or a Princess?

Are the Duke and Duchess Having a Boy or a Girl?
Girl666 (65.2%)
Boy355 (34.8%)