Scarlett Johansson admits to experiencing ''bittersweet'' emotions on the set of 'Avengers 4'.

The 33-year-old actress stars as Black Widow in the Marvel movies, but as the money-spinning franchise looks towards its Post-Phase Three - which includes all the movies made after 'Avengers 4' - Scarlett has admitted to having mixed feelings.

Speaking on the set of the fourth 'Avengers' film, which is due to be released in 2019, she said: ''It's bittersweet to imagine not having these films to come back to. I've been living this story with these people for 10 years through ups and downs. We've built a great family. Personally, it feels like a loss.''

On the flip side, Scarlett has welcomed the recent introduction of new characters and new actors into the Marvel Cinematic Universe, which she believes has breathed new life into the franchise.

She told Vanity Fair magazine: ''We have Brie Larson on this film. She's here before shooting the stand-alone Captain Marvel movie so we get to watch her get her feet wet for real.

''She's so great, but a really cute thing happened the other day where Hulk is standing next to her and [director] Joe Russo told her to put her hand in front of Mark [Ruffalo]'s face to stop him, and she's like, 'In front of his face?' And they explained, 'that's where his chest is,' and she looks up and yells, 'I'm new! I'm new!' I'm like, 'damn, girl.'''

Despite having mixed feelings, Scarlett feels excited about the future of the Marvel Cinematic Universe.

She explained: ''It's very surreal for me to watch these new cast members come in and get their feet wet and breath new life into these characters who are so iconic. I feel a lot of joy for the next generation.

''It's a bittersweet feeling but overall it's a positive one. I feel good about the work we've done and the work I've done.''