"One of my favorite things that I love is when people solve problems in the worst way and it backfires," Prady tells ETonline of Groban's role.
"Piggy is in a foul mood," the showrunner said. "So her ex-boyfriend, Kermit, decides that the best way to calm everything down is to essentially fix Piggy up with somebody, and he does it by going to that list they had when they were a couple -- the free pass list."
For those out-of-the-know, a "free pass list" -- also known as a relationship hall pass -- is a list of celebrity crushes that your significant other is allowed cheat with if the opportunity should ever present itself. That's right y'all -- even Kermit the Frog and Miss Piggy call dibs on celebs!
Although we're not spilling who's on Kermit's list, we will say that you can expect one of his crushes to make a cameo in the episode. (Start shouting out your guesses in the comments below…)
In order to stop his ex's reign of terror, Kermit uses his executive producer power to book Groban on their show, Up Late With Miss Piggy, and engineers an "incredibly romantic" production number. But after the sparks fly, Kermit quickly realizes that he's made a huge mistake.
"[Josh] has ideas about the show," Prady spills. "And then it becomes, 'Well, my new boyfriend thinks this and my new boyfriend thinks that.'" Yikes!
This isn't the first time Groban has worked with The Muppets. This past May, the 34-year-old teamed up with Lindsey Stirling and the entire Muppets gang for the "Pure Imagination" music video, and, looking back, it's clear that Miss Piggy had quite the crush on the crooner.
Groban also appeared in 2014's big screen hit Muppets Most Wanted as a maximum security prisoner in the Siberian gulag.
The Muppets premieres Tuesday, Sept. 22 at 8 p.m. ET/PT on ABC.