Robert Downey Jr. thinks Scarlett Johansson will be a ''great'' mother.

The hunk believes his 'Avengers' co-star, 29, will adapt to motherhood quickly following the recent birth of her and fiancé Romain Dauriac's baby daughter, Rose.

Speaking to E! News, he said: ''I think she's going to be a great mum. Boy, oh boy! I can't believe that she was so pregnant during the filming of 'The Avengers 2'

''Now she finally had the baby so she'll remember those as the good old days.''

Meanwhile, the 49-year-old actor and his 'The Judge' co-star Dax Shepard found out their wives were both expecting a baby at the same time and he admits they have spent a lot of time discussing baby names.

Robert, who is set to welcome a baby girl into the world with his wife Susan Levin in November, said: ''We were talking about names. Yes, very specific names.''

Dax, who will also welcome his second child with Kristen bell later this year, and Robert have bonded over their wives' pregnancy and make sure they keep in contact via Facebook.

Robert confessed: ''I'm part of the social media age now. I know how to work this stuff.''

The star also has sons Indio, 20, with ex-wife Deborah Falconer, and Exton, two, with Susan.