Britain's Prince Harry and his wife Meghan Markle are expecting their second child, their spokesman has said.

"We can confirm that Archie is going to be a big brother," the spokesman said, referring to the couple's son.

"The Duke and Duchess of Sussex are overjoyed to be expecting their second child."

The couple released a black and white image of themselves under a tree with Ms Markle showing signs of pregnancy.

Meghan and Harry, who is Queen Elizabeth's grandson, quit royal duties in March last year and now live in California.

The pair have launched several legal cases against news outlets alleging invasion of privacy - including one that ended on Thursday with a victory against Associated Newspapers in the UK.

The cases have attracted criticism from some, as the couple are also launching themselves into the public eye with high-profile projects such as a Spotify podcast in which Archie made a brief appearance.