Comedian Jim Gaffigan had some advice for Pope Francis when he visited Philadelphia back in 2015, and it wasn't about where to get the best cheesesteak.

Instead, Gaffigan warned the Supreme Pontiff about another Philadelphia cliche: The Santa Claus incident. For the uninitiated, during a game in 1968 Eagles fans booed and pelted Frank Olivo with snowballs after he dressed up as Santa Claus for a halftime Christmas celebration. Olivo died in 2015.

Gaffigan appeared on The Late Show on Friday, where he discussed his experience playing the World Meeting of the Families, where he made a Santa Claus joke, and met Pope Francis, as well as his visit to Philadelphia overall.

"Philadelphia: the City of Brotherly Love,' which, if you've been to Philly, you know they mean that sarcastically," Gaffigan told host Stephen Colbert. "I mean, I love Philly, but they mean that the same way they say, 'Syria: The place for peace.'"

Gaffigan said he added Philadelphia jokes to his act during the event's sound check, and chose the Santa Claus incident because of a short spoof documentary aired by ESPN that focuses on the story.

"I said, 'It's good to be here in Philadelphia,' and I heard a roar from the crowd on the highway, so I thought I'd play to the crowd on the highway," Gaffigan said. "'Philly loves the pope,' and I got another roar. 'Not that I was worried, but you guys weren't that nice to Santa Claus.' Nothing. Silence. And then I heard something that sound like booing, because it was booing. So like 100,000 people booing my Santa joke before they saw their religious leader who was going to talk about mercy."

Gaffigan also said he later got the chance to meet Pope Francis, who he told to leave the Santa thing alone.

"I didn't know what to say," Gaffigan said. "So, when it finally came my turn, I said, 'Don't bring up the Santa incident.' The Pope didn't say anything, but he gave me a look like, 'Dude, I would never bring that up.'"

Gaffigan's latest stand-up special, Cinco, is currently available on Netflix. His Santa story begins at around the 5-minute mark in the clip above.