Martin O'Neill has resigned as Aston Villa manager with immediate effect.
Kevin MacDonald has been appointed caretaker boss while no reason has been given for O'Neill's decision to leave after four years in the job.
MacDonald will prepare the side for their Premier League opener against West Ham on Saturday.
O'Neill, appointed in 2006, said: "I have enjoyed my time at Aston Villa immensely. It's obviously a wrench to be leaving such a magnificent club."
O'Neill, who led Villa to their third successive sixth-placed finish in the Premier League last season and also to the final of the Carling Cup, added: "I would like to pay tribute to the Villa players, my coaching staff and the Villa supporters for all the support and encouragement they have given both the club and me personally during my time as manager.
"I wish them all the best for the future. I will obviously be assisting the club in the immediate short-term with regard to the handover of my duties."
In May, Villa owner Randy Lerner insisted O'Neill had pledged his future to Villa in after much speculation over whether or not the former Celtic boss would quit.
O'Neill has transformed the fortunes of Villa since replacing David O'Leary in August 2006, culminating in an appearance in the final of last season's Carling Cup, their first Wembley final for 10 years.
Lerner had backed O'Neill in the transfer market during that spell but it became clear this summer that similar investment would not be forthcoming.
Lerner insisted that Villa would have to adopt a sell-to-buy policy and O'Neill was resigned to losing the services of midfielder James Milner to Manchester City. Former skipper Gareth Barry also moved to Eastlands last year.
Villa chief executive Paul Faulkner said: "The club would like to thank Martin for the great work he has done at Aston Villa over the past four years.
"He has helped to establish the club in the upper echelons of the Premier League, has taken us to Wembley and we have also qualified for European competition for the past three seasons under his management. We wish him the best in the future."
Randy Lerner aint a billionaire for no reason. Its sensible to adopt a sell to buy policy, although I doubt liverpool would be able to afford to buy young, or tottenham for that matter.
Milners transfer was already going through, so I doubt that was his reason for leaving, however this is not the first time that O'Neill has walked away from a club. Villa will struggle this season imo, with the loss of Milner and possibly Young, and without one of the best managers in the premiership.
TBH its just another casualty of the football merry-go-round, and without a exorbitant amount of money to splash then the majority of clubs are going to struggle. I for one will be welcoming Martin back to his normal role as Tv Pundit with open arms. Roll on the new season!