The Duchess of Sussex, 38, made a last-minute trip to New York to watch the American tennis champion play against Bianca Andreescu last night.
For the occasion, the new mum - who gave birth to four-month-old son Archie in May - chose a belted navy denim dress by J.Crew.
She paired the now sold-out piece, which retailed at approximately £96, with a grey cardigan draped over her shoulders.
The Duchess cheered on her friend - who was ultimately defeated by the Canadian teenager - alongside US Vogue editor Anna Wintour.
Also watching the Grand Slam next to the royal were Serena’s husband Alexis Ohanian, sister Venus Williams and mum Oracene Price.
Prince Harry’s wife had only recently made the decision to fly to the US for the game, it has been reported.
"It is a last-minute trip," a source told The Times. "Excited to support her friend, and then come back."
Meghan had stayed up late to watch Serena win the semi-finals and decided to go watch her friend in person on the spur of the moment.
It is understood the Duchess boarded a commercial flight on Friday accompanied by security but no other staff.
She left the Duke of Sussex at home in Windsor with their baby son.
In June, Meghan stepped out with Kate Middleton to watch Serena play in the women’s final at Wimbledon.
On that occasion, the star also lost to Romanian player Simona Halep.
The Duchess had previously watched her friend triumph earlier in the tournament - but faced criticism over her decision to wear jeans for the occasion.
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