Finn Wolfhard believes he saw a ghost while filming ‘It’.

The actor, 21, who made his name acting in a supernatural hit ‘Stranger Things’, starred in the 2017 movie adaption of Stephen King’s horror book of the same name, and said he is convinced an “electrician” dressed head-to-toe in black on the set he saw with his co-stars was really a poltergeist.

Finn told People: “I’ve been in a lot of supernatural movies and TV shows, but ironically, I’ve never really seen a full-on ghost.

“But there was a time when I was a kid shooting ‘It’ in this abandoned mansion in Toronto, and me and a bunch of the other cast were exploring the floors.

“We went up to the top floor and there was one room where we saw a guy in black just kind of doing electrician work, and we were just like, ‘Okay, that’s just a crew member’.

“But then later, we found out that no one knew who that was, and no one ever saw him again.

“It could have been someone just messing around, but, yeah, it was pretty scary.”

Finn’s other horror projects have included ‘The Turning’ and ‘The Addams Family’ as well as ‘Ghostbusters’ reboot ‘Ghostbusters: Afterlife’.

‘It’ saw Finn play the child version of Richie Tozier – one of a gang of children who call themselves The Losers Club who are terrorised by a demonic being that appears in the form of Pennywise the Clown, played by Bill Skarsgård.

The movie also starred Sophia Lillis, Jaden Lieberher, Wyatt Oleff, Chosen Jacobs, Jack Dylan Grazer and Jeremy Ray Taylor.

‘It’ was the first of a two-part movie adaptation of Stephen King’s 1986 novel, with the first installment followed two years later by 2019’s ‘It: Chapter Two’.

It saw Bill Hader play the adult version of Finn’s Richie character, with Jessica Chastain, James McAvoy, Isaiah Mustafa, Jay Ryan, James Ransone and Andy Bean taking over as the other grown-ups from The Losers Club.