Prince William insists he and his wife Catherine aren't preparing for life as parents just yet, after she was caught doting on a newborn boy at a charity event.

The Duchess of Cambridge, previously known as Kate Middleton, met three-week-old Hugo Eric Scott Vicary on Thursday at an event to mark the achievement of a group of polar trekkers.

Vic Vicary, the boy's father and one of the trekkers, said Kate had "said the baby was very cute, and had doting eyes on him."

Though William later cradled the infant, he dismissed jokes from onlookers that he and his wife were in training for parenthood.

The couple, who celebrate their first wedding anniversary this weekend, earlier made a private visit to the London heaquarters of Britain's overseas spy agency MI6.