St Helens assistant coach Sean Long will leave the club to join rugby union side Harlequins with immediate effect.
Long, 42, is synonymous with the Super League leaders having enjoyed a 13-year playing career at the club, winning two World Club Challenges, four Grand Finals and five Challenge Cups and the Lance Todd trophy three times.
Having coached at Hull, Wigan and Salford before returning to Saints in 2014, he will now leave for a coaching position in the other code.
He said: “I have had 18 memorable years at St.Helens both as a player and as a coach. Working under Justin Holbrook has been a pleasure, but I have always had a desire to work in rugby union and this opportunity at Harlequins is one I cannot let pass me by.
“I want to pay thanks to the whole club, to Eamonn, Mike, Justin, all the players and of course the fans for everything they have done for me. I wish the club all the success this season and beyond and I will always be a Saint at heart.”
Long earned 21 international caps for England and Great Britain during a career which also saw brief spells at Wigan, Widnes and Hull.
At the end of his rugby league playing career, he turned out for Preston Grasshoppers rugby union side.
Mike Rush, Chief Executive at St.Helens said: “I want to thanks Sean for everything he has done at the club both as a player and more recently as a coach.
“He has been a great addition to the club’s coaching team.
“It is with a heavy heart that we have to let him go, but Sean has expressed a desire to work in rugby union in recent months and the club all wish him every success in the future.”