Seacrest has been on "Idol" since the first day in 2000.
"Yes next year will be our final season of @AmericanIdol :( this show's been a big part of my life for so long... hard to imagine it w/out it," he wrote. He then shared a picture from the very first season.
Finally, he wrote that "next season will be emotional yes, but next season will be unforgettable ... i can't wait."
In a statement to Entertainment Weekly, Seacrest, 40, said, "'American Idol' has been a big part of my life for so long, it’s frankly hard to imagine it without it. It’s been a remarkable journey, and I feel very fortunate to have been part of a show that made television history in countless ways. It’s a show about chasing and fulfilling dreams, and truth be told, it helped some of my own dreams come true too."