LONDON (Reuters) - Britain?s Prince William and his wife Kate are expecting their third child, their office said on Monday after the Duchess was forced to cancel an engagement due to severe morning sickness. The couple, who released the news via their office at Kensington Palace, did not say when the baby was due. ?The Queen and members of both families are delighted with the news,? the palace said. Britain?s monarchy has ridden a wave of public support in recent years due to the emergence of the younger royals, William, Kate and William?s brother Harry.