EXCLUSIVE: Liam Neeson Gushes Over 'Absolutely Real' Performance by 14-Year-Old 'A Monster Calls' Co-Star

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A Monster Calls star Lewis MacDougall might only be 14 years old, but he will have a long career ahead of him if co-star Liam Neeson has anything to say about it.

"He was real, absolutely real," Neeson told ET. "The scenes I had to do and his emotions, I don't know how he reached them. They were unbelievably believable and made me think, 'How does that kid manage that without appearing to act?'"

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The upcoming drama follows 12-year-old Conor (MacDougall) as he attempts to deal with his mother's illness and the bullying of his classmates until one day he is confronted by a monster in the form of tree (voiced by Neeson) and escapes into a fantastical world.

MacDougall revealed that he was able to draw on his own personal tragedies to prepare for the role.

"My own mother passed three years ago so, although the two experiences were completely different, it did give me a bit of understanding as to what he was going through," he said.

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While Neeson was in awe of MacDougall's performance, the newcomer also gave a glowing review of the veteran star's work.

"He has such an amazing voice, but the key thing to remember is that it's not just his voice," he said. "The reason why we're doing the motion capture is because it captures his movements, not just his voice acting. I think he did a fantastic job."

A Monster Calls opens Dec. 23.