COLUMBUS, Ohio — Ohio State football coach Ryan Day and Chip Kelly have officially come full circle, with the program announcing the latter’s hire as offensive coordinator and quarterbacks coach Friday night.

Day’s previous hire, Bill O’Brien, departed Friday after a mere three weeks to become Boston College’s head coach. Instead of being knocked off course, Day quickly pivoted to his friend and mentor who — in an unprecedented move — left his position as head coach of incoming Big Ten member UCLA to serve as Day’s play-caller.

Ohio State said Kelly agreed to a three-year deal.

“We are extremely excited to have Chip and his wife, Jill, joining our program,” Day said in a news release. “His experience as a head coach at Oregon, UCLA and in the NFL will bring immediate value to our entire team. I am really looking forward to reconnecting with Chip, introducing him to our staff and team and chasing a championship together.

“I would also like to wish coach Bill O’Brien and his family well as he takes over at Boston College.”

The Manchester, New Hampshire, natives first connected 25 years ago. Kelly was an assistant and Day the quarterback for the state university’s Wildcats. Day later served as Kelly’s quarterbacks coach with the Philadelphia Eagles (2015) and San Francisco 49ers (2016).

While their roles have reversed, Kelly represents a crucial source of experience and stability for Day, who is stepping away from play-calling duties for the first time.

Kelly rose to prominence at Oregon, with a two-year stint as offensive coordinator and four years as head coach. His up-tempo attack and high-scoring offenses made his reputation as an advanced offensive thinker and tactician. That led him to the NFL, where his first two Eagles teams won 10 games, including an NFC East championship in 2013.

Kelly’s last three UCLA teams went 25-13. In many ways his resume mirrored that of O’Brien, who Day selected specifically due to his NFL experience and head coaching background. The difference is Kelly and Day share even more commonality, both in their background and their offensive philosophies.

Brian Hartline will continue to serve as co-offensive coordinator with Kelly, as was planned under O’Brien.