© GettySerena Williams has been friends with Meghan, the Duchess of Sussex for years.
Serena Williams has revealed Archie Mountbatten-Windsor has already visited the US, secretly travelling with his mother in September.
Speaking to Access Hollywood about her adoration of the Duchess of Sussex, a friend of several years, Williams mentioned Meghan had brought Archie with her during her whirlwind visit to New York.
"She flew all the way with a newborn to see me play in New York and flew all the way back that night, and I probably couldn't have done that," the tennis star said.
"It kind of goes to show you what an amazing person that she is, and that's just one of the many things that she does for me."
The Duchess travelled to New York to see Williams play in the US Open final on September 8, flying via commercial airline in the wake of the couple's private jet controversy.
The former Suits star attended the match without her husband Prince Harry, and at the time it was reported Archie was with his father in the UK.
Williams and Meghan have been close friends since meeting at a 2010 Super Bowl party, and have navigated motherhood and married life in the years since.
The Grand Slam champion was one of the stars who helped the Duchess celebrate her flashy baby shower in New York earlier this year and is rumoured to have organised the event. © PA/AAPThe tennis superstar let slip baby Archie came to the US with his mum to watch Serena play tennis in New York.
The pair have also leaned on each other in difficult times; earlier this year, it was reported Meghan had been going to Williams for support amid an onslaught of nasty comments on the Sussexes' social media pages.
"I just really think she's the strongest, literally the strongest person I know and the nicest, sweetest," Williams added.
"I call her, text her anytime, crying, upset - she's always there.
"Doesn't matter what she's going through, she just sets time away and she's just so amazing."
Pictures: Prince Harry and Meghan's trip to Africa