England international centre Michael Shenton will leave Castleford Tigers at the end of the season, the club have confirmed.
Shenton, 24, is out of contract at the Jungle and is expected to join engage Super League rivals St Helens.
"We would have liked to have kept Michael and made him a big offer to stay," said Castleford coach Terry Matterson.
"However, he has made a decision to move on which we respect and we are very grateful for his contribution in what will have been seven seasons with the club.
"Michael is also a real professional and I know that he'll be as keen as anyone over the remaining fixtures to help us win us a place in the top eight."
Shenton, who came through the junior ranks at his home-town club, turned down the chance to join Bradford several years ago in order to remain loyal but now looks certain make the move across the Pennines.
Castleford are hoping that promising teenager Joe Arundel will help fill the void and they demonstrated their confidence in the youngster by giving him an extended contract to the end of 2012.
Arundel, who made his Tigers debut as a 16-year-old in 2008, deputised for Shenton in the club's recent win at Salford and hopes to return from a leg injury for Sunday's trip to Crusaders.
Matterson said: "On the back of Richard Owen re-signing, we're really pleased that Joe has also agreed to stay with the club for another two years.
"He has pushed his way into first grade this year and looked very comfortable. I'm very excited about what Joe can do for Cas in the future and we are hoping to see him available for selection for Sunday's game in Neath."
Arundel, a product of the Tigers' youth development programme, said: "I always wanted to stay with Cas so I'm pleased to have got this new deal sorted out.
"Breaking into the squad this season has been a plus and hopefully I can keep my place this year."