Scarlett Johansson is “madly in love” with her son Cosmo.

Scarlett Johansson

Scarlett Johansson

The ‘Black Widow’ star gave birth to her baby boy last week, and sources have now said she and her husband Colin Jost are “so happy” with their new arrival.

Cosmo is the first child for Scarlett and Colin together, but the 36-year-old actress is also mother to six-year-old Rose, whom she has with her ex-husband Romain Dauriac.

An insider said: "They are very private but elated over the baby. They are both so happy and madly in love with the baby.

“They wanted this child who will fit right into their lives since they already have her daughter. They are an awesome couple, both talented, smart and clever. They will be the best parents."

The source also insisted Colin, 39, is being a “considerate and helpful” father so far, and said Cosmo’s arrival is “the best thing ever” for the couple.

They added: "Colin is considerate and helpful in everyday life so adding one more to the mix should be fine. The baby is the best thing ever for both of them."

And the ‘Saturday Night Live’ star is helping his wife through the “stress of a newborn” with “quick wit” and “a great sense of humour”.

The insider told People magazine: "Each has a great sense of humour which will help with the added duties and stress of a newborn.

“[Colin’s] quick wit will help them through sleepless nights and any other issues that arise with a baby. Being able to laugh together is a great marital asset. Having great communication helps when this added layer of responsibility enters their lives. They are happy. And now is a good time to get used to their new lifestyle."

Colin confirmed his baby’s arrival last week.

He wrote on Instagram: “Ok ok we had a baby

“His name is Cosmo

“We love him very much

“Privacy would be greatly appreciated (sic)”