LONDON — Britain doesn’t have to wait any longer: Prince William’s wife, Kate, is pregnant.

St. James’s Palace made the announcement Monday, saying that the Duchess of Cambridge — formerly Kate Middleton — has a severe form of morning sickness and is currently in a London hospital. William was at his wife’s side.

The news drew congratulations from around the world, with the hashtag “royalbaby” trending globally on Twitter.

The couple’s first child will be third in line to the throne — behind William and his father, Prince Charles — leapfrogging the gregarious Prince Harry and possibly setting up the first scenario in which a female heir could benefit from new gender rules about succession.

The palace would not say how far along the 30-year-old duchess is, only that she has not yet reached the 12-week mark.

Palace officials said the duchess was hospitalized with hyperemesis gravidarum, a severe form of morning sickness that affects about 1 in 200 women and can lead to dehydration or worse if left untreated. They said she was expected to remain hospitalized for several days and would require a period of rest afterward.