Guess which big Serena Williams fan just touched down in New York to see the GOAT play the U.S. Open final today? Duchess of Sussex Meghan Markle!

One of Serena's best friends and biggest supporters, Meghan is SUCH a fan that she left 4-month-old baby Archie for the first time to go and support Williams. Meghan took a commercial flight out of London Friday early morning. She headed straight to a yoga class to help with jet lag, according to People.

It's not Markle's first trip since giving birth -- the family of three headed to the Spanish island of Ibiza this summer to celebrate her 38th birthday. After that they headed to Nice in the south of France. The trio are set to visit South Africa, touching down in Capetown on Sept. 23. Baby Archie will largely be out of the spotlight since he's so young. The royal couple will use the trip to highlight "a modern UK-Africa partnership in action," according to the couple's personal secretary who held a press conference about the upcoming trip at Buckingham Palace Friday morning.