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Meghan Markle supported her good friend, tennis star Serena Williams at the U.S. Open Finals on Saturday.

The royal mom was all smiles in Williams’ box at Arthur Ashe Stadium, where she sat in front of Anna Wintour and behind Williams’ husband Alexis Ohanian, to watch her friend play against Bianca Andreescu in the final.

The outing marks the Duchess of Sussex’s first trip overseas without her 4-month-old son, Archie. On Friday, Meghan, 38, made an unexpected last-minute trip aboard a commercial flight from London, PEOPLE confirmed. Prince Harry remained home with their son in Windsor.

The royal’s last trip to America was in February for her baby shower with close friends.

Meghan first met Williams at the 2010 Super Bowl in Miami where they immediately hit it off. Last summer, the tennis pro and her husband Alexis Ohanian, who both attended the royal wedding, joined Meghan to watch Harry compete in a polo match in Ascot, England. Williams also helped throw a baby shower for her friend in N.Y.C.earlier this year.

In July, Meghan and some friends watched Serena’s match at the Wimbledon championships. She then joined sister-in-law Kate Middleton for the women’s final.

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Meghan is expected to return to Britain at the end of the weekend. “It is a last-minute trip,” a source told The Times, which broke the story of the royal’s plans. “Excited to support her friend, and then come back.”

Williams said that having Meghan’s support and friendship “is great,” telling reporters during her post-match press conference in July: “She’s such a great friend and a great person as well. And always positive, no matter what.”

The tennis star continued, “It’s so good to have people like that, just to know,” adding that Meghan, 37, is “such a fan of the sport.”

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In a recent interview, the tennis star shared that she is refraining from offering parenting advice to Meghan for now.

“I never pass on words of wisdom because I feel like everyone, when they have a kid, especially when you just have a baby, it is so difficult to just be,” Williams told BBC Breakfast ahead of Wimbledon. “And it’s just like, get through the first three months, four months, and then we can talk.”