"Southampton Football Club can today confirm it has accepted the resignation of first team manager Ronald Koeman, and completed negotiations with Everton over his move to Goodison Park," the statement read.
"The search has already begun for the right appointment who can take the club to the next level and build on our track record of recent success, which culminated in a sixth-place finish in last season's Premier League, as well as qualification for the group stages of the Europa League.
"Our focus now is to build on our long-term plan, and work with a new management team who share both the club's and our supporters' values and ambitions."
Southampton FC & London Lions in Betfair's Tap Tap Boom Challenge
Former Ajax boss Frank de Boer, interviewed by Everton, is just behind at 5/2.
Ex-Tottenham manager Andre Villas-Boas, who left Zenit Saint Petersburg in May, is at 15/2.
Fenerbahce coach Vitor Pereira and ex-Manchester City boss Manuel Pellegrini are both at 8s, while former manager David Moyes is also in the frame at 14/1.
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