The Duke and Duchess of Cambridge are expecting their second child in April next year, Kensington Palace has said.
The pregnancy had already been announced but the due date had not been released.
The duchess will make her first public appearance on Tuesday since her pregnancy was announced in September.
She will join Prince William to officially welcome Singapore’s President Tony Tan as he begins a four-day visit to the UK.
The duchess will also attend the Wildlife Photographer of the Year 2014 awards ceremony at the Natural History Museum in London.
The duke and duchess’s second baby will become fourth in line to the throne, behind older brother Prince George, who was born in July last year.