The Marvel star has become a mum for the second time. Photo / Getty Images

Colin Jost has confirmed he and Scarlett Johansson have welcomed a son named Cosmo.

The 'Saturday Night Live' star and the 36-year-old actress welcomed their first child together, after Scarlett – who is also mother to six-year-old Rose, whom she has with her ex-husband Romain Dauriac – gave birth "recently".

And while Scarlett's representative Marcel Pariseau confirmed the news to People magazine with no further details, Colin took to Instagram less than hour later to announce their new arrival is a baby boy called Cosmo.

He wrote: "Ok ok we had a baby. His name is Cosmo, we love him very much. Privacy would be greatly appreciated."

The news comes just days after Colin, 39, confirmed the 'Black Widow' actress was pregnant during a stand-up performance at a theatre in Connecticut.

He told the audience: "We're having a baby, it's exciting."
Scarlett's pregnancy was first reported last month, when sources said she was due "soon".

One insider said: "Scarlett is actually due soon, I know she and Colin are thrilled."

Another added: "Scarlett is pregnant but has been keeping it very quiet. She has been keeping a very low profile."

Scarlett had sparked speculation she was pregnant again for weeks before the sources spoke out, as she hadn't been involved in many in-person events to promote 'Black Widow'.

Instead, she made virtual appearances, such as a Zoom interview with 'Tonight Show' host Jimmy Fallon in June, on which she was only shown from the shoulders up.

A separate insider claimed: "She hasn't been doing many interviews or events to promote 'Black Widow' which is surprising since it is a huge Marvel/Disney release and she is both the star and an executive producer."