Prince William with wife Kate PIC: John Stillwell/PA Wire

The Duke of Cambridge Prince William celebrates turning 30 today with private party at St James’s Palace in London.

A royal spokesman said it would be a “low-key” and “private” function.

No more details about how the Duke will celebrate leaving behind his 20s were revealed.

Wife Kate (nee Middleton), who turned 30 in January, is thought to be behind any plans.

She must also find a present for her husband, no small task when he is second in line to the throne of England.

William’s 30th birthday is an important milestone for the royal who could one day be King.

The Duke is a happily married man who wed Kate, his university sweetheart, during a glittering ceremony last year watched by an estimated television audience of billions.

He is also forging ahead with his RAF career, and earlier this month it was announced the royal had qualified as an operational Captain and can now command RAF Sea King helicopters during rescue missions.