Celtic captain Scott Brown vowed to be "relentless" in his quest for success with Aberdeen after accepting an offer to become a player-coach at Pittodrie.
The 35-year-old has agreed a pre-contract deal and will join up with newly-appointed Dons boss Stephen Glass, his former Hibernian team-mate, in the summer.
The decision will bring a hugely successful 14-year spell at Celtic Park to a close.
The midfielder has won 22 trophies, made 613 appearances – including a club-record 127 games in Europe – and scored 46 goals. He has been captain of the club for 11 years.
In a statement released by Aberdeen, Brown said: "There is no doubt I had a lot to deliberate when deciding my next steps, particularly after enjoying 14 successful years at Celtic.
"However, the opportunity to join Aberdeen, a club entering an exciting new period with my former team-mate Stephen now at the helm, was one I couldn't pass up.
"Once this season concludes, I'm looking forward to joining Stephen, the playing and coaching staff and everyone at Aberdeen FC. I am totally committed to the challenge that lies ahead in meeting the ambitions of the club and its fans.
"I still feel I have got a lot to give, not only on the pitch, but in a broader capacity as I embark on my coaching journey. I will be relentless in my quest for success for Aberdeen."
Brown has made 38 appearances this season but came under serious competition for his place from Ismaila Soro in December, and has chosen to move on with Celtic seeking a new manager.
The 55-cap former Scotland international declared that Celtic would always be in his heart.
In a statement on the Celtic website, he said: "It was a privilege to sign for this great club all those years ago and it has been an absolute honour to play for and captain Celtic for so many years."
Thanking chief executive Peter Lawwell, principal shareholder Dermot Desmond and the board for their "tremendous support", he added: "We have always enjoyed a great relationship and always worked closely together to bring our fans as much success as possible.
"I would also like to thank the great Celtic managers I have had the good fortune to work with and also so many team-mates and, of course, the Celtic fans who have given me such phenomenal support and backing over the years.
"I have always given my best to the club and always wanted the best for our fans.
"We have enjoyed some fantastic moments and success together, dominating the game in Scotland so regularly and enjoying some great European nights.
"It is a huge decision to leave this magnificent club, which has been such a massive part of my life for so long, but this is a new opportunity for me and a new chapter.
"Celtic will never leave me and the club will forever be in my heart.
"We still have work to do this season and that will of course, as ever, be my full focus as we try to bring our fans more success."
