While in London to promote the upcoming “X-Men: Dark Phoenix” movie, stars Jessica Chastain and Sophie Turner couldn’t stop talking about Chastain and co-star James McAvoy’s other movie, “IT: Chapter 2”.

After McAvoy, who plays the now grown-up character of Bill in the sequel, told ET Canada the horror film left him with “sleepless nights,” Chastain was left to ponder whether she could use his nightmare fuel against him.

“Mac Attack told you he had nightmares and he couldn’t sleep?” she asks. “I mean we were filming in very scary sewers.”

“Are they real sewers that you’re filming in?” her “X-Men” co-star Turner replies. “No, it was built,” Chastain says, adding, “but the water was disgusting.”

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But when it comes to who is more terrifying – “It: Chapter 2” clown Pennywise or Turner’s X-Men character Dark Phoenix – there’s no contest.

“Pennywise eats children,” Chastain says.

“And I don’t think Dark Phoenix would eat children,” Turner responds. “I hate him. I hate him. I also saw that teaser trailer of you and the old woman… running around naked. Ugh, I hated it so much.”

While Chastain is looking ahead to “It” this September, Turner is happy to have said her goodbyes to “Game Of Thrones”.

“It’s you know 10 years of my life that I loved so much but it took up a lot of time during each year and so it’s great to know that you know you have full years ahead that you can fill with your little projects that you probably wouldn’t have been able to do on ‘Game of Thrones’ so its quite liberating and it’s exciting,” she says of the end of the series. “I do feel like I’ve graduated.”

“X-Men: Dark Phoenix” opens int theatres on June 7.