Graeme Souness has quit as Blackburn Rovers manager to take over at Newcastle United.
Blackburn have revealed Souness has left the club and that he has agreed terms to succeed Sir Bobby Robson.
Souness said: "I'm sad to be leaving but I'm excited. I'm joining one of the biggest clubs around."
He will take charge on Monday 13 September, after Newcastle's game against Blackburn on Saturday, although he leaves Ewood Park immediately.
Souness added: "Newcastle is one of the best-supported clubs around. It is a club where everything is there to be successful and I just hope I'm the man to bring it to them."
Blackburn have appointed long-serving Tony Parkes as caretaker manager for the sixth time.
Newcastle had targeted Birmingham's Steve Bruce and Aston Villa manager David O'Leary.
O'Leary appeared to be favourite for the job after Bruce insisted he would be staying at St Andrews.
But Souness, regarded as an outsider for the post, is taking over at the troubled Tyneside club after talks with chairman Freddy Shepherd.
Blackburn chief executive John Williams said: "My reading of the situation is quite clear.
"Graeme is very reluctant to leave a job he considers one of the best in the business, but he views Newcastle as a massive opportunity and one he cannot resist.
"But now is the time to look forward and we need to focus all our energies on finding Graeme's successor.
"We have an excellent squad of players and have a lot to offer the new manager, not least a financially stable club, and we expect considerable interest in the position.
"It is time to move on, we know what we are looking for and anticipate a very strong list of applicants."
Newcastle striker Craig Bellamy said: "I don't particularly know about Graeme Souness's managerial style, but it's up to me now to prove myself again."
Souness is understood to have told Blackburn's players he was leaving the club when they arrived for training on Monday morning.
Former Liverpool manager Gerard Houllier has been touted among the early contenders to replace Souness at Blackburn.
Souness, a 51-year-old Scot, was a former star player at
Liverpool and he also managed the Merseyside club.
He was also manager at Rangers, Galatasaray, Southampton, Torino and Benfica before taking over at
Blackburn in March 2000.