Celtic have announced that chief executive Peter Lawwell will retire at the end of the season.
Lawwell, 61, has held the post since 2003, overseeing 13 Premiership titles and four domestic trebles at Parkhead.
Scottish Rugby's chief operating officer Dominic McKay will take over from Lawwell in July. McKay was promoted to the role of CEO in 2015.
"It has been an enormous privilege to have served the club and our supporters for more than 17 years – a wonderful honour to have been part of an institution I have loved and supported all my life," Lawwell told Celtic's website.
"I will always be very proud of what we have achieved together and it has been a particular privilege to be involved throughout a period in the club's history which has brought immense domestic success – as well as so many great European nights at Celtic Park.
"Everything we have aimed for and achieved has been for everyone associated with the club.
"Celtic's reputation is built on three pillars – success on the field of play, sound business management, and a real and sincere charitable ethos, building on the club's founding traditions.
"My objective has always been to maintain and strengthen all three in order to ensure that the club is both successful in the short term and in the long term, and is handed down to future generations in the best possible condition."
Celtic, the nine-in-a-row champions, are currently 23 points behind league leaders Rangers with three games in hand.
Lawwell added: "I first discussed the possibility of my retirement with the chairman last year and we were keen to ensure an orderly handover to a new CEO once we had found the right candidate.
"Now that the process to select Dominic McKay as my successor is complete, I feel the time is now right to announce my retirement at the end of this season.
"I believe the club have identified an excellent successor with the highest integrity who will bring substantial experience and enthusiasm to the role.
"Like every Celtic supporter, I am disappointed that, so far, this season has not worked out in the way we all hoped for, despite our best efforts.
"My goal will be to work with Dominic in order to make changes as smoothly as possible and maintain a focus on continued success on the field of play. Together, our main priority will now be to ensure a seamless transition."
Celtic Chairman Ian Bankier added: "On behalf of the Celtic Board of Directors, I would like to thank Peter for his monumental contribution to Celtic and its success during the past 17 years.
"Peter has given his life to our cause during his term of office, delivering a period of unprecedented success to the club on and off the field.
"He will be regarded as a man who has played a pivotal role in our history and we should always respect the huge impact he has had on the club."
Following the announcement of his new role, McKay told the Scottish Rugby website: "Joining Celtic FC as chief executive is a once in a lifetime opportunity and a new challenge I am very excited about taking on later this year.
"I have been incredibly impressed with the vision and people within the club and I look forward to working with them."
He added: "I can honestly say I have enjoyed the best 13 years of my life at Scottish Rugby and made life-long friends across the sport and all its numerous Unions, partners, broadcasters and sponsors.
"It has been a huge privilege to work with such a talented and passionate group of people over this time. "
