Katy was the first judge who signed on for American Idol's upcoming revival on ABC, which premieres March 11, and then Luke followed suit.
"I heard that Luke was coming on and we were all wondering what the third position would be, and I was really gung-ho about Lionel coming in from Day 1," Katy revealed to E! News.
Lionel was completely flattered at the time, saying he was "blown away" to hear Katy had been pushing for him.
"I actually made the call, and was like, 'It's Lionel Richie,'" Katy insisted.
"Because I saw him out at dinner one time... We crossed paths [and it] was one of those things where it got extended by two more hours because he was just telling us all these stories. It's so interesting because you hear about your legends, and he's got stories on all of them!"
"By the time I left, I was like, 'I think she got a word in,'" Lionel joked.
"But the point was, we bonded. And Luke, of course, I've known from before, and we met and had an instant southern-boy connection, right away. So it was one of those great moments in life when we found out we were together on the show, forget about it, this is the best."
"This is the recipe," Katy noted with a big smile.
Lionel called judging contestants on American Idol's sixteenth season an "extension of my hobby." He said that since the judges themselves are successful artists, they know enough to either boost an aspiring singer's ego or provide a reality check.
"[We'll say] 'What can I do to help you,' or, 'What can I say to let you know that this is not your career?'" Lionel explained, before Katy threw out the word "delicately."
Katy said each judge speaks his or her mind when critiquing the hopefuls, but Luke is especially "sweet" while she is more "cut and dry" with a short attention span.
"The stakes are high, especially these days in the music industry. I'm a super-realist and we only want stars. I understand people are coming in with so many hopes and dreams, but you have to have the talent first, and then the hopes and dreams happen," Katy told E! News.
But Lionel insisted, "It's so exciting because we really hit the jackpot in real life, and we get to give this opportunity to someone else. And we know exactly how it feels... [If a singer is not ready], there's no way of making it puffy, puffy. I got to tell you in five seconds, 'It's not happening!' Experience is what we bring to the table, and I love that!"
Luke didn't say much during the joint interview, but he assured fans joining the American Idol cast was never about advancing his own career. Instead, he wants to have fun and "mentor and help these kids" to potentially change their lives.
However, besides Season 10 winner Scotty McCreery, the former Fox reality singing competition has experienced a drought in which more recent winners haven't enjoyed much commercial success after the show.
American Idol therefore found it increasingly more difficult to trump its TV competitors, such as The Voice, and the series came to an end in early 2016 before ABC opted to resurrect it.
American Idol is set to premiere with a two-hour episode at 8PM ET/PT. The show, once again hosted by Ryan Seacrest, will air on Sunday and Monday nights starting March 12.