When Joseph Gordon-Levitt was working his way to his A-Lister status, Bruce Willis gave him the “highest compliment” possible, and it still resonates with him today.

The Third Rock From the Sun alum has starred in many blockbuster films throughout his career, including Oscar-winning films Lincoln and Inception. But he gave his personal favorite performance in Looper.

In the 2012 sci-fi thriller, Gordon-Levitt plays the younger version of Bruce Willis’ Joe. Joe is a time-traveling hitman tasked with going backward a few decades to kill his younger self. While Gordon-Levitt is arguably the movie’s lead, Willis was the star. And Gordon-Levitt wanted to ensure his character was the perfect tribute to his counterpart without being an exact copy.

While talking in a Vanity Fair retrospective last year, Joseph Gordon-Levitt explained why the role was so special to him.

“One of my kind of marks of success as an actor myself is, ‘Do I seem different on screen from myself.’ It’s probably why Looper’s maybe my favorite performance of mine because it’s the most different,” he said. “I did a lot of work to try to do my vision that wasn’t an imitation of Bruce Willis but had sort of the spirit of Bruce Willis, and if I had to pick a favorite just acting-wise, this is up there for me.”

Bruce Willis Surpised Joseph Gordon-Levitt With a

And Joseph Gordon-Levitt wasn’t the only person who thought his acting was spot on. While filming an intense scene with Bruce Willis, Willis offered the young star some “validation” with a small compliment that hit him in a big way.

“There was another scene later in the movie where we were yelling at each other,” he remembered. “I don’t know if Bruce did this on purpose or if he did it unintentionally, but it was kind of the highest compliment he could pay me.”

“It was right after they said ‘Cut,’ he was turning away and walking back to his mark,” he continued. “He didn’t even say it to me; he just kind of said to himself, ‘Sounds like me.’ And I just turned to myself and went, ‘F**king yes!’”

Gordon-Levitt noted that writer and director Rian Johnson made it clear that while he and Willis were technically playing the same character, there should be a difference between a younger and older man. So knowing that Willis thought Gordon-Levitt nailed it meant everything.

“I think knowing him, that was really his ultra-generous way of paying me a compliment,” he continued. “But it was very kind to do it in that way.”