Serena Williams said she understood the "pain and cruelty" suffered by Meghan, the wife of Prince Harry, after she accused Britain's royal family of racism.

Meghan, in an interview with Oprah Winfrey aired on CBS late on Sunday, said the royal family had concerns about how dark their son's skin might be.

The 39-year-old, whose mother is Black and father is white, also said she was pushed to the brink of suicide after marrying into royalty in 2018.

Williams, a Black woman who has won 23 Grand Slam titles, said her "friend" Meghan had taught her "what it means to be truly noble".

"I know firsthand the sexism and racism institutions and the media use to vilify women and people of colour to minimise us, to break us down and demonize us."

"The mental health consequences of systemic oppression and victimisation are devastating, isolating, and all too often lethal."

Meghan and Harry said in the interview their second child, who is due this summer, would be a girl.

"I want Meghan's daughter, my daughter, and your daughter to live in a society that is driven by respect," Williams added.