The spokesperson said: "We can confirm that Archie is going to be a big brother. The Duke and Duchess of Sussex are overjoyed to be expecting their second child."
Harry and Meghan are preparing to welcome a brother or sister for their son Archie Mountbatten-Windsor, who turned one last May.
A spokesperson for the couple said they were "overjoyed" at the news.
The couple shared a black and white picture of themselves under a tree, with Harry resting his hand on Meghan's head as she cradles her bump.