James Corden has often called his Carpool Karaoke episode with Paul McCartney his all-time favorite. However, in a recent conversation at the Paley Center for Media, Corden revealed just how challenging it was to keep McCartney on board for the segment. He described the process as “thrilling,” but also filled with hurdles.

Although McCartney was already familiar with the concept of the show, the two weren’t strangers, making it easier to pitch. Initially, McCartney was excited, telling Corden, “I’m in, I’ll do it, I can’t wait.” But things quickly took an unexpected turn when, just a month later, McCartney pulled back, saying he had cold feet. Corden recalled receiving a message stating, “He’d canceled, he didn’t want to do it.”

The drama didn’t end there. Days before their planned trip to Liverpool, Corden got another email from McCartney’s team, stating that once again, he was backing out, citing that it wasn’t the right moment for him.

Despite the setbacks, McCartney eventually agreed to go through with the segment, and it went on to become one of the most iconic episodes in Carpool Karaoke history. Corden elaborated on the unforgettable experience in the rest of his interview.