Britain's Catherine, the Duchess of Cambridge, arrives with her husband Prince William, as they prepare to open a children's cancer unit at the Royal Marsden Hospital in Sutton, in south-east England, on September 29, 2011. AFP PHOTO/BEN STANSALL

Britain's Catherine, Duchess of Cambridge, (R) Prince William (C) and Prince Harry, (L) leave after attending the wedding between England rugby player Mike Tindall and Britain's Zara Phillips, granddaughter of Queen Elizabeth II, at Canongate Kirk in Edinburgh, Scotland, on July 30, 2011. AFP PHOTO / BEN STANSALL

(FILES) In a file picture taken on June 13, 2011 Catherine, Duchess of Cambridge, smiles as she watches the procession at the Order of the Garter Service at St George's Chapel in Windsor Castlein Windsor. Catherine, Duchess of Cambridge, turns 30 on Monday after a near-faultless nine months of low-key royal engagements as she makes a gentle entrance into royal life alongside her husband Prince William. AFP PHOTO / POOL / KIRSTY WIGGLESWORTH