The pair will walk down the aisle next year (11) and William's younger brother is expected to act as best man. Harry admits he couldn't be more ecstatic at the news.
A statement from him reads, "I am delighted that my brother has popped the question! It means I get a sister, which I have always wanted."
Prince William, who is second in line to the British throne after his father Prince Charles, has been dating Middleton for eight years after they met while studying at Scotland's St Andrews University.