"Our little man arrived! Jack Oscar Statham 8.8lbs on Saturday June 24th," she captioned a photo of his hand, which she posted on June 28.
It's the first child for the couple.
The supermodel and the action star announced they were expecting in February when she shared an idyllic photo of herself on the beach and in a bikini. In the image, taken by her beau, her baby bump was fairly pronounced.
"Very happy to share that Jason and I are expecting!!" she captioned the image. "Lots of love Rosie x."
At the time, there was speculation that she was pregnant. Rumors began after she posted an image to Instagram on Jan. 2 of her petting a horse.
"Here's to fresh starts and exciting prospects for the new year. Wishing everyone a happy and healthy 2017..❤," she captioned the image.
Becoming a mother was always something she wanted to be.
"Having a family is something I think about for sure, and whether I'd live here in America or England. But it's not always as simple as that," she said in 2015. "I have no idea what will happen, but it'll be interesting to find out, right? And nothing will be perfect, I'm sure."