Ruan Pienaar will leave Ulster at the end of the season after being unable to agree a new deal with the Irish province.
Both the province and the player were "keen for him to extend his stay in Belfast" but an extension was "not possible due to the IRFU's succession policy".
"I am not moving on for a new adventure or for financial reasons - I wanted to stay and I know that Ulster Rugby did everything it could to keep me in Belfast," Pienaar said in a statement today.
"Ulster is special to me and my family now, and I would like to thank my wife, Monique, for coming here to support me and for helping to make it home for us.
"I would also like to thank all of the players and staff at Ulster Rugby, the supporters and the general public, for their support and encouragement since our arrival. It has been brilliant to see the progress that the organisation has made in recent years, particularly with the new facilities here at Kingspan Stadium. The club has given me a lot and I'd like to be in a position to give something back in the future if possible.
"I have many great memories of my time here and I have made some brilliant friends within rugby and outside of it. It is sad that this will be my last season as an Ulster player but I will be doing everything to ensure that we make it a successful campaign."
The South African played a vital role in the team that reached the Heineken Cup final in 2012 and Ulster head coach Les Kiss lamented the loss of "an outstanding servant" to the province.
"His influence within the squad, both on and off the field, is truly remarkable; whether that is through match-winning contributions, or mentoring the promising players coming through our pathway. Indeed, he has played a big part in helping us to develop a large group of talented young backline players who have gone on to represent Ireland in recent years.
"Ruan has been an outstanding servant to Ulster Rugby over the past six years and he will be a huge loss for us next season.
"For me, he is a fantastic player, but he is an even better person, who is much-loved by his team-mates, the staff and management, and the wider rugby community here in Ulster.
"He is a consummate professional and I have absolutely no doubt that he will give everything to the Ulster cause for the rest of the season. Our hope is that he will one day return to the Province to continue to have a positive impact on rugby in Ulster."
Pienaar has scored 777 points in 118 competitive games for Ulster to date and Ulster Rugby chief executive Shane Logan said they will miss his contribution in the future.
"Ruan's exploits on the pitch are well-documented, but perhaps his biggest contribution since his arrival in Ulster has been his work with the local community. He has been freely giving of so much of his time and he has helped to inspire young people across the Province, not only in rugby, but in their everyday lives. That impact is something that cannot be easily measured.
"We have continued to show that we have the resources, and more importantly, a positive environment and ethos, that makes us an attractive proposition for prospective players. This culture was one of the main reasons why Ruan, among others, was attracted to the club in the first place and why he was so keen to stay.
"I, personally, will miss having him around Kingspan Stadium, but I am looking forward to seeing what he will deliver for us over the course of this season, and the door is open for a return in the future."
