The private couple, already parents to 20-month-old Esmeralda, welcomed daughter Amada Lee Gosling at 8:03 a.m. on Friday, April 29, in Santa Monica, California. The birth comes less than a month after PEOPLE confirmed Mendes was pregnant.
Reps for the actors did not immediately respond to request for comment.
Shortly after news of her pregnancy broke, the actress, 42, was spotted stepping out in Los Angeles, where she was seen holding her bag in front of her belly.
Mendes, who similarly managed to keep her first pregnancy under wraps for several months, "just hasn't ever wanted anyone beyond her close friends and family knowing more than they had to," an insider previously told PEOPLE.
And according to insiders, Gosling is not the type to spill the beans either. "Ryan is certainly private and always has been," the source added.
The actor was recently spotted out in Palm Springs in March, where he and Mendes celebrated the actress's 42nd birthday by renting Frank Sinatra's old vacation house. While Gosling was photographed around town, there were no sightings of Mendes, or any potential signs of a baby bump.
Mendes's social media accounts have also offered no hints of a bump, as the actress hasn't posted any recent photos of herself in weeks.
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Before meeting Gosling, Mendes had said she was not planning on getting married or having children, but "with Ryan things are different," a friend told PEOPLE. "She's very independent, but she's content with her partner. She finally found the person she really wants to be with."
Gosling expressed similar feelings in an interview with Hello! magazine, saying, "I know that I'm with the person I'm supposed to be with."
The famous couple have kept their daughter out of the spotlight since her birth, but a source previously told PEOPLE that Gosling is "madly in love" with Esmeralda, and Mendes is loving her life as a new mom.
"She's never been happier," the source said of Mendes. "She and Ryan are just in awe of this beautiful person they created. It's a really special time for them."