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Britains' Prince William interacts with members of the 3rd Battalion, Royal Australian Regiment during his unofficial visit to Sydney, Wednesday, Jan. 20, 2010. ( AP Photo/Rick Stevens, Pool)

Britain's Prince William

Britain's Prince William, the oldest son of Princess Diana and Prince Charles, turned 31 on June 21. The prince, also known as the Duke of Cambridge, is expecting his first child with wife, Catherine Middleton.