Tennis superstar popped in to see baby Archie at Frogmore Cottage last week, making a flying visit before heading to Paris to compete in the French Open.
Ms Williams, 37, was joined by her husband Alexis Ohanian, 36, and their one-year-old daughter Olympia.
The seven-time Wimbledon champion, posted a picture of herself in a regal state room at the Windsor home of Harry and Meghan, who she is close friends with.
Tennis superstar popped in to see baby Archie at Frogmore Cottage last week, making a flying visit before heading to Paris to compete in the French Open. Above: Serena even posted a picture of herself in a regal state room on Instagram before getting back to work yesterday
Ms Williams was a guest at Meghan's wedding to Prince Harry, and reportedly co-hosted her £330,000 baby shower in New York in February.
The tennis star was helped in her hosting duties of the glitzy event by Meghan's best friend, Canadian fashion stylist Jessica Mulroney, 39, and the Duchess's sorority sister Genevieve Hillis.
The event was held in the The Mark hotel's incredible Grand Penthouse Suite, which costs a staggering $75,000 per night, making it the most expensive hotel room in the US.
Ms Williams, who is a close friend of Meghan, was a guest at her wedding to Prince Harry and reportedly co-hosted her £330,000 baby shower in New York in February
Star guests included Amal Clooney, American CBS Anchor Gayle King, and actress Abigail Spencer.
Ms Williams and Meghan first met at a Super Bowl party in 2010 and have been friends ever since.
Meghan wrote of their first meeting on her now-closed blog The Tig, and said: 'Taking pictures, laughing through
