PICTURE: Britain's Catherine, Duchess of Cambridge receives flowers from three-year-old Isobelle Laursen during her visit to Peaks Lane fire station in Grimsby, northern England on March 5. Reuters/Bruce Adams

The wife of Britain's Prince William, the Duchess of Cambridge, might have accidentally revealed the sex of her unborn child during a conversation with a well-wisher, hinting that the future monarch could be a girl.

When presented with a white teddy bear on a trip to Grimsby in northern England, a woman in the crowd said Kate appeared to hint that she was expecting a daughter.

"I distinctly heard Kate say: 'Thank you, I will take that for my d...'" Sandra Cook, who was standing next to the woman who presented Kate with the toy, was widely quoted as saying.

"Then she stopped and corrected herself to say... 'for my baby'," Cook said.

The slip provoked front page coverage in the British media with intense speculation on whether Kate is carrying a future queen.

William, whose father is heir to the throne Prince Charles, married Kate in April 2011, and the couple's movements attract huge interest around the world.

A spokeswoman for William's office said they had no comment on reports about the baby, due to be born in July.

Britain and other Commonwealth countries which have Queen Elizabeth as their monarch have agreed to change the rules of royal succession so that males would no longer have precedence as heir to the throne. – Reuters