Although method acting is not really his style Culkin brother proved that there is no substitute for authenticity – especially when it comes to stage props.

In a 2012 re-interview. Mark Ruffalo shared a crazy story about a "naughty young actor" who mistook a fake stage joint for the real thing during a live performance, leaving him unexpectedly high in front of the audience.

Now, years later, one of the Culkin siblings has finally come forward and admitted that they were the mastermind behind the prank.

Kieran Culkin made his debut together with his brother Macaulay Culkin in the iconic 1990 holiday film Home Alone, playing Kevin McCallister's mischievous cousin Fuller. He repeated this role in the film "Home Alone 2: Lost in New York". Shortly after his Hollywood debut, he appeared in the 2000 Playwrights Horizons production of James Lapine's The Moment When, opposite Mark Ruffalo.

With a stockpile of props in the background, Culkin couldn't resist the temptation to replace one. “Uh-oh. I believe that happened,” he thought a few weeks later as he caught a familiar scent and “just watched” Ruffalo hit before passing it to their co-star.

During the break, Culkin felt compelled to confess. “I'm like, 'I thought this was a good joke. I'm stupid. Oh my God, I'm so sorry,' he said The Guardian. “But actually, they loved it. Mark says: 'I haven't smoked weed in 10 years; the second half will be a lot of fun.' There was another actor who never smoked weed in his life. She says, 'Is that being high? This is wonderful.' And then Phyllis Newman comes along and says, 'I haven't smoked weed since the 1960s. Thank you, dear.'”

Culkin continued: "Then the stage manager comes in and says, 'I don't care whose it is or what happened, but Kieran, give me the joint.' He sheepishly handed over the remains. "She said, 'Ruin your life in your own time.'"

The Golden Globe winner seems to have taken the experience to heart. “I was 17 years old and stupid... I was young. I am now 42 years old. I know better. I'm not going to try to lift someone up on stage,” he said.

"There was a play I did where I had to smoke a joint in the first scene," he said at the time. "And of course there was a very naughty young actor I was in a show with who, on opening night with all the critics, dropped a real joint on the props table."

Known for being totally committed to his performances, Ruffalo admitted, “So when you're at a party, you take two breaths and say, 'Okay, that's enough. I'm so high.' But I was acting, so I was like...” he said, mimicking an exaggerated intake of breath. "Between the two of us, we smoked a giant blunt on stage."

As the scene played out, Ruffalo recalled feeling unstoppable. “And I'm like, 'Man, I'm in it tonight. I can feel it. I'm on fire. I can feel it... why is that guy standing backstage laughing at me?'" Then he realized that the young actor responsible was standing offstage and shooting. "And I just said, 'Oh shit.'"

But there is a silver lining to the story. Ruffalo added with a smile, "But at the end of the show, I got the best reviews of my entire career."

Kieran Culkin rose to global fame with his role as Roman Roy in HBO's acclaimed series "Succession." Playing the sharp-witted, irreverent youngest son of media mogul Logan Roy, Kieran became a fan favorite for his biting humor and vulnerable portrayal of a deeply flawed character. His performance earned him multiple Emmy and Golden Globe nominations, and he won the 2024 Golden Globe Award for Best Supporting Actor in a Series.

Kieran Culkin has firmly established himself as one of Hollywood's most versatile and compelling actors, proving time and time again that he is much more than "Macaulay's younger brother".