Colin Farrell has heaped praise on his The Killing of a Sacred Deer co-star Barry Keoghan, saying he is "a great actor and a great human being".

25-year-old Keoghan has been receiving rave reviews for his work in the film, which was written and directed by The Lobster's Yorgos Lanthimos and won the Best Screenplay award at the Cannes Film Festival.

Keoghan, who starred in Christopher Nolan's Dunkirk earlier this year, plays a troubled teenager in the film who begins to have a dark affect on Colin Farrell's character's life.

Speaking about Keoghan, Farrell told RTÉ Entertainment, "He's doing amazing, he's having the most amazing year or two, and long may it continue.

"He's deadly, I love him. He's a great actor and a great human being and I wish him all the luck in the world."

Colin Farrell and Barry Keoghan at the Cannes Film Festival

The dark nature of the film had an impact on both Farrell and Keoghan, with the two actors experiencing sleep troubles while filming.

"I remember when Barry said he was starting to dream, which is great, I mean, it's not great, it's not good craic when you're dreaming about this material but it just means that your subconscious, or unconscious, has suited up and is on the playing field," Farrell said.

"I did, I had wicked dreams and I didn't sleep very well during the making of this. I don't sleep super well anyway, but worse than ever. You don't lose yourself, it's not like I was going around like I had no idea who I was, or at home telling my children to call me by my character's name and s***, but I was a bit depressed by the end of it, yeah."

The Killing of a Sacred Deer hits cinemas on November 3.

Watch our full interview with Colin Farrell here: