Millwall have announced that they have reluctantly accepted Kenny Jackett's resignation as manager.
Millwall have endured a mixed season, reaching the FA Cup semi-final but only averting relegation from the Championship on the final day of the season.
Jackett, who guided the Lions to promotion from League One in 2010, is seeking a "new challenge" after six years with the club and chairman John Berylson expressed disappointment that the 51-year-old had decided to move on.
"On behalf of the board of Millwall Football Club, I want to express my thanks to Kenny for his fantastic service and achievements over the past five and a half years," he told the club's official website. "He has played a major role in creating a stable environment at Millwall which hadn't been the case prior to his arrival.
"On a personal level, whilst respecting Kenny's decision, I wish I could have persuaded him to change his mind. He was my first acquisition as chairman of the club and has proved himself to be one of the best. I am losing a great manager, but he will remain a good friend and, hopefully, golf partner.
"I know everyone associated with Millwall, management, staff, players and fans, will wish Kenny all the very best with his future endeavours, except for those times when he might oppose us on the pitch. We are now determined to move the club forward and build on the foundations Kenny has provided towards even greater success."
Jackett, who has previously managed Watford and Swansea, added: "After almost six seasons I personally feel the time is right for a new challenge, and also for a new manager to come into Millwall with fresh ideas, to take the club forward towards its long-term goal of reaching the Premier League.
"I would like to thank the chairman, the board of directors, players, members of staff and supporters of Millwall for their considerable backing. I have thoroughly enjoyed my time at Millwall. My family and I will always have a strong link and affinity with the club."