Mariah Carey will perform one of her classic songs, "Hero," just before the clock strikes midnight on New Year's Eve, one year after a televised performance mishap that left the singer "mortified."
"New year [is] about new beginnings," Seacrest said. "She’s a legendary, iconic artist so we’re excited to have her back to do it again."
After Carey left the stage, she tweeted that "s--- happens."
Her camp later claimed that the TV production staff dropped the ball when it came to making sure her in-ear monitors worked; a rep for Dick Clark Productions denied any implication that the company would "intentionally compromise the success of any artist."
"I’m of the opinion that Dick Clark would not have let an artist go through that," Carey told Entertainment Weekly at the time. "He would have been as mortified as I was in real time."
Seacrest called Carey an "old friend" and said, though he didn't have the idea to bring her back, he is glad she is returning to the show.
"It’s not my idea but it’s a good idea," Seacrest said. "I think people are excited to see her back. People love her. She’s beloved."
"I think it’s going to be an amazing moment with her," he said.
Seacrest, who will share hosting duties again this year with Jenny McCarthy, said he is mostly worried about the near-record low temperatures expected in New York City on Sunday night.
Revelers could be in store for the coldest ball drop since 1962 in Times Square. ABC News is forecasting a temperature of around 10 degrees with a wind chill of minus 4 when the calendar turns to 2018.
"It’s terrifying," said Seacrest, who recently relocated to co-host "Live with Kelly and Ryan." "I’ve had it pretty easy. I’ve lived in Southern California for so many years. I’m now in New York full-time so I’m getting used to it."
Once 2018 begins, Seacrest will be off and running in his role as host of the new "American Idol."
ABC is bringing back the long-running music competition series with a premiere in March. Seacrest served as host for the franchise since its 2002 debut.
"That show is so special to me," Seacrest said. "I talk to a lot of people around the country that, you know, they grew up watching the show. They were born, watched it and waited to be old enough to participate in the auditions and when it went away they were so bummed they couldn’t and now it’s back and they can. [There are] so many great stories like that.
ABC News' Andrea Dresdale contributed to this report.