Hull Kingston Rovers have parted company with head coach Craig Sandercock with immediate effect, midway through his third season in charge, reports BBC Radio Humberside.
A club statement confirmed: "The club has made the decision not to renew Craig's contract in 2015.
"With that in mind we have placed Chris Chester in charge of first-team duties, initially until the end of the season."
The 45-year-old Australian has been in negotiations with the club for weeks.
Chairman Neil Hudgell was keen to keep Sandercock in charge for a fourth season at Craven Park.
Hudgell told BBC Radio Humberside that he had offered the coach a new one-year contract which remained unsigned, while Sandercock indicated only last week to the BBC that he did not foresee any problems.
Rovers have have only had two coaches since entering Super League in 2007.
Justin Morgan left at the end of the 2011 season, after six years in charge, having enjoyed his most successful campaign in 2009 when Rovers finished fourth.
They finished 10th in his first season at the helm in 2012, and then scraped into the play-offs last year.
This season they currently stand ninth, three points outside the all-important top eight, but a point better off than city rivals Hull FC.
Assistant coach Chester will take charge for the first time in Sunday's home game against league leaders St Helens, to whom the Robins have not lost at Craven Park in six seasons.