Josh Taylor's split from Cyclone Promotions was "a huge surprise and a killer blow", says the Scottish boxer's former trainer Shane McGuigan.
IBF and WBA super-lightweight champion Taylor, who had been with Cyclone since turning professional in 2015, signed with US outfit Top Rank this month.
Shane, son of Cyclone head Barry McGuigan, will no longer train the 29-year-old and says his exit rankles.
"I feel a bit begrudged by it all," he told Boxing Social.
"It was late December and I got a phone call saying Josh was asking to leave. It was a pretty big shock. I didn't see anything coming.
"As soon as I heard that, my heart sank. Mainly because of the effort and time that we had put in to Josh. I felt we had managed him and trained him impeccably - 16 fights unbeaten, unified world champion, Ring magazine champion.
"To find out like that was a blow. I'm annoyed that I've invested four-and-a-half years of my time and energy in someone who just doesn't deserve it."
Taylor's departure has soured relations with the stable where he made his name.
Cyclone insisted he had broken an "exclusive worldwide contract" with them, while the Prestonpans fighter responded by claiming the company's "various breaches of contract" enabled him to walk away for a multi-fight deal with Top Rank.
In the ring, their partnership culminated with Taylor's World Super Series final triumph over Regis Prograis in October, making him the unified IBF and WBA super-lightweight champion.
"We were in regular talks with JT about a multi-fight deal with Matchroom USA and DAZN and Sky," McGuigan added. "We were constructing something really big for him. Obviously he chose to do his own thing.
"If he'd been a year into his career, fine, no problem. And if he'd have called me and talked to me and everyone and done it the right way, then that would have been fine.
"I train fighters that aren't necessarily managed by my dad. But with Josh, dad had signed him from the start and has done an amazing job with him.
"It's not right to do it that way. I'm not going to continue to train him when he has done that to somebody so close to me. I just feel it's not fair for that person to be cut out."
Josh Taylor previously gave his take, stating that he wanted to part ways amicably... Read more...