Crystal Palace have described manager Tony Pulis' departure as being by 'mutual consent'.
First-team coach Keith Millen will take temporary charge for the Eagles' opening Barclays Premier League match against Arsenal on Saturday.
Pulis was appointed manager in November and led Palace to survival, an achievement that earned him the Premier League manager of the season award just three months ago.
The Eagles picked up just seven points from their opening 12 games but Pulis' arrival instigated a remarkable turnaround as the team finished 11th in the table and 12 points clear of the drop.
Pulis' departure reportedly stems from disagreements with co-chairman Steve Parish over the club's transfer policy.
Palace have so far signed former Blackpool goalkeeper Chris Kettings, Martin Kelly from Liverpool, Fraizer Campbell from Cardiff and Brede Hangeland from Fulham but failed to finalise deals for the likes of Gylfi Sigurdsson, who returned to Swansea, and Steven Caulker, who joined QPR.
Pulis' relationship with Parish was strained during the initial period after he took charge, but the former Stoke boss insisted at the end of last season he was not unhappy at the club.
"That's nonsense,' Pulis said.
"In the first couple of weeks Steve and I had our moments but the longer the season has gone on the closer we've got.
"Our relationship, which I think is the most important at a football club, has got more and more solid.
"I had a fantastic relationship with my last chairman at Stoke - the way we thought and worked things out was one of the main reasons why that club was so successful.
"It's something you have to nurture and bend at times to make it work and that's what Steve and I have done."
Former Cardiff boss Malky Mackay has been installed as the early favourite to succeed Pulis, with Tim Sherwood, Neil Lennon and David Moyes also considered possibilities.
Palace announced in a statement on their website on Friday: "Crystal Palace Football Club can confirm that Tony Pulis has left the club by mutual consent with immediate effect.
"Keith Millen will be in temporary charge of the team for our opening Barclays Premier League game against Arsenal this Saturday.
"The club would like to thank Tony for his efforts with the club during last season and wish him all the best for the future."