The new royal baby is due next April, it has been announced by the Duke and Duchess of Cambridge.
Kensington Palace also said the acute morning sickness that has afflicted Catherine during the pregnancy is "steadily improving".
Pregnant Catherine will make her first public appearance for some time tomorrow (21 October), it was confirmed. She will join husband Prince William in welcoming the President of Singapore to Britain.
Prince William has appeared alone at engagements due to his wife suffering from the condition known as hyperemesis gravidarum.
The new baby will be a sibling for Prince George and will be fourth in line to the throne, behind his or her brother, father and grandfather.
Prince George was born in July 2013 after a pregnancy during which the Duchess also suffered severe morning sickness.
More to follow.