The pregnant actress celebrated with friends in the Parisian-inspired tea room, enjoying lush desserts and treats to mark the special occasion.
She wore a black slip dress with bow-tie straps, and accessorised her low ponytail with a black bow headband with a ring of pearls in the centre. Very Blair Waldorf from Gossip Girl.
The cake and the room were adorned with celebratory decorations exclaiming: "It's A Boy!"
Jessica revealed she was expecting a baby boy during an interview with Jimmy Fallon in October, where she hilariously revealed the names she refuses to give her son.
Jessica and her husband of nine years, Cash Warren, shared the happy news that they were expecting in an Instagram post in July.
The actress proudly posed with her two daughters, 9-year-old Honor Marie Warren and 5-year-old Haven Garner Warren, holding numbered balloons.
"Cash and I are officially going to be outnumbered," she wrote at the time.