The second-in-line to the throne is expected to mark his birthday privately with his wife the Duchess of Cambridge, née Kate Middleton, and their son Prince George.
In honour of William's special day, HELLO! Online brings you ten facts about the Prince.
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1. William's full title is His Royal Highness Prince William Arthur Philip Louis, Duke of Cambridge, Earl of Strathearn, Baron Carrickfergus, Royal Knight Companion of the Most Noble Order of the Garter.
2.The Prince is a big fan of British singer Ellie Goulding, whom he asked to perform at his and Kate's wedding. He has also admitted he is a fan of Justin Bieber. "I enjoyed the Justin Bieber song, Never say Never, but it's not my favourite."
3. He is a supporter of the arts and in 2010 he became the new president of the British Academy of Film and Television Arts (BAFTA).
4. In 2013 the royal became a father for the first time when he and the Duchess of Cambridge welcomed their son Prince George.
5. When asked what he would do if he was invisible for the day, he said "I'd probably go into the newspaper office and listen to all the stories they tell about me."
6. The royal shares his birthday with Killers' singer Brandon Flowers and Lana Del Rey.
7. Former royal cook Darren McGrady revealed the future king has a sweet tooth.
"William loved ice-cream and would eat it sitting in the kitchen windowsill, chatting away," he explained. "He was also very fond of banana flan."
8. At the time of writing, there are 6,785 items listed under 'Prince William' on eBay UK, with items including Christmas cards, figurines, glossy post cards and royal wedding spoons.
9. In early 2014 it was announced William would be leaving the British armed forces after more than seven years to concentrate on supporting his grandmother, The Queen and the Duke of Edinburgh.
Since leaving, the Prince, Kate and George have undertaken a three-week visit to Australia and New Zealand.
10. Determined to continue his mother's legacy, William has become passionate about the charities he supports, and in 2009 spent a night sleeping rough on the streets near Blackfriars Bridge in central London to raise awareness for homeless charity Centrepoint, of which he is patron.