The Bourne Identity star shared her baby announcement with her 131k followers on Instagram, and since sharing the sweet snap has garnered 17k likes and over 417 comments.
The touching photo of her husband holding a tiny newborn hand also reveals the baby's name: 'Strummer Newcomb Cook, born October 20, 2017.
'Thanks and ever thanks to the extraordinary Doctors, Nurses and staff at Mount Sinai for helping bring this utter joy into our lives ❤️✨,' Julia continued. 'Hello, World!'
The congratulations from fans quickly rolled in, with one writing: 'Hello Little Person, welcome to the world! Congratulations!'
'Awe Julia I am so happy for you and your family! Welcoming a baby into the world is the most beautiful thing you will ever do! How in the world did you keep this secret for over a month? Congrats btw,' exclaimed another, while a third fan said: 'Cannot believe it!!! Amazing Julia! Welcome to motherhood, you are gonna rock it!'
The pair met in 2015 on the set of the film Go With Me, where Preston was working as a cameraman.
A few months after they began dating, Julia opened up to The Guardian about their relationship. Replying to the question of 'what was your best kiss ever?', she said: 'It might have happened this morning. I am dating a camera assistant I met at work called Preston.'
The couple got engaged on Christmas Eve of the same year, and in September 2017 confirmed that they had tied the knot in what Julia referred to as a 'shotgun wedding'.
An intimate snap from their wedding shared on social media showed Preston's hand, complete with his new wedding ring, affectionately placing his hand on his new wife's bump.
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