Celtic captain Scott Brown has signed a pre-contract with Scottish Premiership rivals Aberdeen in a player-coach role.
The Pittodrie club confirmed that the 35-year-old former Scotland skipper will move north in the summer.
Brown, who will join new manager Stephen Glass' backroom staff after 14 years at Celtic, said it was "a new chapter" in his career.
Glass, who is moving from Atlanta United 2, said Brown's arrival signals a "coup" for Aberdeen.
Brown is added to Glass's staff after Aberdeen parted company with Derek McInnes earlier this month.
"The opportunity to bring a player of Scott's calibre, a leader who has more European appearances for Celtic than any other player, is a huge coup for me and for Aberdeen," said Glass.
"A born competitor, with a strong appetite to win, his hands-on approach and desire to nurture will hugely benefit the development of the young, emerging talent we have here.
"Scott will be a big part of my coaching team and whilst his impact will undoubtedly be felt on the pitch where I believe he still has much to give, I am looking forward to assisting his transition into coaching."
Brown, who signed for Celtic from Hibernian in 2007, amassed more than 600 appearances for the Glasgow side, winning 10 league titles and 12 domestic cups.
'A new opportunity'
"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," he told Celtic's website.
"Celtic will never leave me and the club will forever be in my heart."
Looking forward to his future challenges at Pittodrie, Brown added: "The opportunity to join Aberdeen, a club entering an exciting new period with my former team-mate Stephen [Glass] now at the helm, was one I couldn't pass up."
Outgoing Celtic chief executive Peter Lawwell said the club had tried to keep Brown and described the midfielder as the most influential figure in Scottish football in the past 15 years.
"He has been a pivotal figure in delivering such a sustained period of dominance for the club and for that, I know every Celtic supporter will be so grateful to him," said Lawwell.
"It goes without saying that we were desperately trying to keep Scott at the club, but while of course we are very saddened by his decision, we understand and respect it fully and wish Scott and his family nothing but success, health and happiness for the future."