For the first time in Idol history, the longtime host will be handing over his hosting duties to the show's in-house mentor, country music radio personality Bobby Bones, Peoplereported.
However, this casting change is temporary, as Seacrest reportedly came down will an illness when the two-hour episode taped a few weeks ago and he didn't feel healthy enough to participate.
People obtained an exclusive clip of Monday night's episode in which Bobby announces he'll be taking over for Seacrest.
"I am not Ryan Seacrest," Bones, 39, says. "I am Bobby Bones. Sadly, Ryan is sick and I look most like him so they asked me to fill his shoes tonight. Ryan, love you, buddy, hope you get better."
Bones then goes on to announce the second round of celebrity, All-Star duets.
"Man, do we have a lineup for you tonight," Bones continues, according to the magazine. "We are joined by six singing superstars who will be teaming up with our super talented contestants for some show-stopping duets."
Seacrest reportedly revealed on his morning radio show, On Air with Ryan Seacrest, that he gifted Bobby -- who just celebrated his birthday on April 2 -- a pair of shoes with the following note: "Thanks for filling my shoes."
"Bobby was kind enough to fill in for Monday's episode which we taped a few weeks ago," Seacrest explained, "and I'm thinking, you know, the guy stepped in last-minute, did a great job. What do I get him? I got him some shoes!"
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American Idol has never had a host other than Seacrest or Brian Dunkleman -- who only co-hosted Season 1 -- since the reality singing competition debuted on Fox in 2002.
Monday night's episode will feature 10 of the Top 20 contestants performing duets with famous singers.
The Top 14 contestants will eventually get to sing for America's votes.
In Sunday night's episode, the judges advanced the first set of seven contestants to the Top 14: Walker Burroughs, Riley Thompson, Uchechukwu "Uche" Ndubizu-Egwimis, Madison Vandenburg, Ashley Hess, Laci Kaye Booth and Laine Hardy.