She shared her relief at coming to the end of the UK press tour and not having let anything slip, but didn't hold back when Digital Spy asked which co-star was the worst at keeping secrets.
"Mark Ruffalo is the worst at keeping secrets," she told us and others. "He is embarrassingly bad at keeping secrets... I think they've got him under control now. He's a security risk for sure."
Tom Holland got off lightly there....
The actress was attending the special fan event for Avengers: Endgame with Chris Hemsworth and Paul Rudd in London last night (April 10).
Ruffalo recently revealed that Marvel bosses were actually happy when he accidentally leaked Thor: Ragnarok footage.
"That was the one that got me the call from up high," he said.
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The Hulk actor then admitted that the Marvel team were delighted by the blunder because of the audience's positive reaction to the films opening.
"It sort of turned around on me, because when I came to work on Monday [on the set of Endgame] everyone ran up to me," Ruffalo recalled.
"I thought they were coming to scream at me – [Marvel security] Barry [Curtis], he threw his arms around me. 'That was genius! We got more press than we could have possibly paid for!'"
Avengers: Endgame is released in UK cinemas on April 25 and US cinemas on April 26.
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