is shedding a new light on how he feels about his 2013 duet with .

During his on the  After Show, the "Gravity" singer was asked to name his least favorite album. And while John picked —noting he liked some of its songs but that he spent the least amount of time on this album and others were more important in his life— applauded its track "" featuring Katy. And the Grammy winner agreed it's a good song. 

"Isn't that great?" John replied. "I'm glad we did that."

Likening it to "early prototype stuff," the 45-year-old then shared his thought-process behind the song.

"It was just at the point where I was saying, 'Why can't I make music from a different era? If I love a style of music and I want to make it, like a genre, why can't I make music that I was pretending was from a different era?'" he continued.

"And that was sort of like a prototype to . It was sort of like an FM lite radio thing, and is a little more realized."

And ultimately, John had nothing but praise for Katy on the track.

"But I listen to that every once in a while, and I go, 'I like that song,'" he added. "And I like the way that she sounds on the song. She got that way of singing down and met the challenge of that song. It was so much fun."

John and Katy first sparked in 2012 following her divorce from . The "Daughters" artist and the "Firework" singer continued to have an until they .

In fact, John previously hinted that his 2017 song "Still Feel Like Your Man" is a nod to his split from Katy, who is now engaged to

and shares 3-year-old daughter with the actor. 

"Who else would I be thinking about?" John told in 2017. "And by the way, it's a testament to the fact that I have not dated a lot of people in the last five, six years. That was my only relationship. So it's like, give me this, people."

(E! and Bravo are both part of the NBCUniversal family).