This marked the first time the duo had seen each other since filming the 2012 series finale, during which Taylor's character Jenny Humphrey returned to New York City and Penn's character married longtime on-again/off-again girlfriend Serena van der Woodsen, who was portrayed by his real-life ex, Blake Lively.
And although that might seem awkward—filming a fake wedding scene with your ex—Penn doesn't recall any tension. In fact, off-camera, Blake had actually tied the knot with Ryan Reynolds three months before the Gossip Girl series finale aired.
"From my memory, I'm pretty sure we were exes for nearly half of the run of the entire series," Penn—who reportedly began dating Blake in 2007—shared on the Sept. 6 episode of Podcrushed. "It lasted for nearly six years and I don't think we were together longer than two? Something like that."
"We were always very professional," he continued. "We had to do all kinds of nutso stuff. Having a fake marriage by the end of it...I don't even think, in my memory, there was not one bit of strangeness. It wasn't even a thing."
As Penn—who is now married IRL to Domino Kirke—also pointed out, the drama revolved around relationships of some form.
"All of us had been in every configuration imaginable," he said of the cast, which also included Leighton Meester, Ed Westwick and Chace Crawford. "The finale, in a lot of ways, felt a little bit to me like, after such a long time, it was almost an afterthought. It was revealed that I'm Gossip Girl and Dan and Serena get married."
Penn also spoke out about his former romance with Blake earlier this year, sharing how the relationship helped to ground him amid Gossip Girl fame.
As the 36-year-old told Variety in February, while the six-season run of the show was "fun and fast-paced" it also had "dark undercurrent" that affected him in his late 20s.
"To be honest, I never struggled with substance," the You actor shared. "Blake didn't drink, and I think our relationship in some ways saved me from forcing myself to go down that road."
To hear Penn share more about his behind the scenes experience on Gossip Girl, listen to his chat with Taylor on Podcrushed.