“Dave, thank you for everything!” Scarlett Johansson promotes Avengers: Age of Ultron while praising Letterman.

Scarlett Johansson has her new life as a mother to talk about and a blockbuster Avengers movie to promote.

But the Hollywood superstar made it clear she only had one thing on her mind when she appeared on Monday night on The Late Show With David Letterman – her love of the chat show host himself.

After a comically awkward introduction where Letterman said the movie star’s beautiful white dress looked ‘like an old-fashioned linen table cloth’, Scarlett, 30, repeatedly made a point of praising the chat show legend who will soon retire.

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Praised the host: Scarlett Johannson praised David Letterman on Monday during her appearance on The Late Show on CBS

‘Dave, I have to say, I am so incredibly honored to be on one of your very last shows,’ Scarlett said, making sure she got her praise in before he could star questioning her.

‘The first time I was on this show I was 13-years old, it was 1998 and I was so, so nervous, because for me – and still for me – coming on this show is like you’ve made it when you’re on Dave Letterman. That’s really the truth,’ she said.

Recalling that first time, promoting The Horse Whisperer, she joked about how the host ‘gave me a canned ham and my dad kept it in the fridge until I was 25 and it walked out on its own, practically’.

Warm welcome: Letterman kissed Scarlett’s hand during her visit to the late night chat show

But she insisted: ‘Coming on this show has been kind of like the milestone of my career every time.

‘Thank you for everything Dave! There’s never going to be anybody like you,’ she gushed.

She returned to her love for the host when he teased her that he didn’t ‘know why you’re here’ because the movie she was promoting, Avengers: Age of Ultron, has ‘already made $200 million’.

First appearance: Scarlett first appeared on the show in May 1998 to promote The Horse Whisperer

‘I know – I just came to see you, actually,’ she replied, getting appreciative sighs from the audience while she made a heart symbol with her hands.

Scarlett had her biggest smile of the night while talking about her seven-month-old baby Rose, saying her middle name was Dorothy in ‘homage to my lovely, lovely grandmother’.

But she seemed taken aback by Letterman’s dark questioning about her world views now that she’s a mother.

New movie: Scarlett has been promoting her upcoming superhero film Avengers: Age Of Ultron

‘Don’t you worry – you take a look at the world and think, “Ooh, I’ve brought this perfect human being into this world, will she be alright – will the world treat her well?”’ he asked.

After a pause, Scarlett said: ‘Oh my God, that’s so heavy.’

When he continued – telling her ‘you’re never free of that thought, are you’ – she again replied with surprise, saying: ‘Wow, gosh, really?’

Good times: Scarlett laughed while chatting with the chat show host who will be retiring soon

‘I haven’t slept in so long Dave – I don’t know what to say,’ she finally laughed.

‘I’m just a new mom – cut me some slack.’

When she finally said that she looks at her daughter ‘and sees a little environmental lawyer so she’s going to fix everything’, Letterman joked: ‘You look at your daughter and think she’s going to be part of the solution – and I look at my son and know better.’

She’s back: Scarlett looked thrilled to be returning to the show

The actress did not do such a good job promoting the movie, admitting that she did not know what the Age Of Ultron even meant ‘until the premiere night’.

Then after a fumbled explanation, she said: ‘I’m sorry Marvel, that was such a bad sell.’

Scarlett introduced a clip showing her on a motorcycle as Black Widow in a scene with Captain America.

Show clip: Scarlett apologised to Marvel for her attempt to sell the blockbuster that already has made $200 million overseas

‘You were on a motorcycle when you were seven months pregnant?’ Letterman asked.

‘No, obviously not,’ Scarlett replied.

The clip turned out to be a gag reel featuring an old black and white clip of a woman being chased by a remote-controlled robot.

Letterman asked how much longer she expected to carry on playing the Black Widow.

‘As long as I look good in a cat suit, I guess,’ she said, joking: ‘So probably about seven months.’

That’s funny: The actress and host enjoyed several laughs during their time together