Julia Stiles shows off baby boy three weeks after birth

Actress Julia Stiles is a new mom.

The Bourne Ultimatum star and her husband Preston J. Cook welcomed their first child back in October (17), but kept the baby news quiet for weeks.

Stiles took to Instagram on Tuesday (21Nov17) and posted a shot of Cook holding his son's hand.

"Strummer Newcomb Cook, born October 20, 2017," she wrote alongside the photograph. "Thanks and ever thanks to the extraordinary Doctors, Nurses and staff at Mount Sinai for helping bring this utter joy into our lives."

It is not yet clear which Mount Sinai hospital the actress is referring to.

Stiles was heavily pregnant with little Strummer when she and Preston quietly exchanged vows over Labor Day holiday in September (17) on a beach in Seattle, Washington.

"Who doesn't love a shotgun wedding?" she captioned a photo of the newlyweds on their big day, with her proud bulging baby belly on full display, three weeks after they became husband and wife.

A representative for the 36-year-old actress confirmed reports she was expecting her first child back in June (17), and while promoting her new U.K. TV series Riviera at the time, Julia told SKY News, "I'm expecting a human being. I'm very excited."

Stiles and Cook met on the set of 2015 film Blackway. He was a camera assistant and she was among the stars, along with Sir Anthony Hopkins and Ray Liotta.

Cook popped the question during a Christmas vacation on Colombia's Isla Grande in 2015.