Tennis star Serena Williams says she's "proud" of Meghan Markle following her interview with Oprah Winfrey.

Williams called Meghan "my selfless friend" in an Instagram post after the sit-down aired Sunday night in the U.S. praising the Duchess of Sussex as "brave."

"I know it is never easy," Williams said in the caption. "You are strong- both you and Harry."

Meghan revealed in the interview that she experienced suicidal thoughts after joining the royal family. She also said there were concerns within the palace while she was pregnant with son Archie about how dark his skin might be.

Williams said Meghan's words "illustrate the pain and cruelty" Meghan has experienced.

"I know first hand the sexism and racism institutions and the media use to vilify women and people of colour to minimize us, to break us down and demonize us," Williams wrote. "The mental health consequences of systemic oppression and victimization are devastating, isolating and all too often lethal."

Williams said she wants her daughter, Meghan's daughter and "your daughter," referring to readers, "to live in a society that is driven by respect."

Meghan and Harry announced during the interview that they are expecting a daughter.