Model and actress Molly Sims is a mum again.

The Yes Man star welcomed her third child with her film producer husband of five years, Scott Stuber, on 10 January (17).

Little Grey Douglas Stuber joins four-year-old brother Brooks and their baby sister Scarlett May, one.

Sims took to Instagram today to announce the baby news and share the first photo of her son.

"Welcome to the world Grey Douglas Stuber 1.10.17," she captioned a shot of herself and the newborn. "Words do not express how grateful and happy we are to have another piece of magic added to our little tribe!"

Sims recently revealed she is desperately trying to convince her husband to get a vasectomy, because she doesn't want a fourth child.

At 43, her latest pregnancy has been more stressful than ever, and Molly is not prepared to go through it all again, so she has asked Scott to get 'the snip'.

"My husband is getting a vasectomy, but he doesn't know it yet," she joked to Momtastic. "He's fighting me on it. But there's not going to be like, 'Oh, this was an accident!' No. It's happening."

Molly announced her pregnancy in August (16) and as her due date neared, she admitted she was feeling a mix of emotions.

"I'm excited but I'm also nervous," she shared. "I worry about Scarlett more than Brooks because she is used to getting all the attention as the baby in the family. At the same time, I can only do the best I can do. I'm giving them a present - another sibling that they'll have for life. But it's definitely nerve-racking. It's nerve-racking to be older and delivering, too."