Bournemouth coach Eddie Howe left the club by mutual consent after leaving the Premier League.
The 42-year-old led the Cherries in more than 450 games in two periods of more than a decade.
The Englishman, who leaves after talking to club officials on Saturday, said he believed "it is the right time for the club to change".
Bournemouth's five-year stay in the top flight ended despite 3-1 win at Everton on the last day of the season.
"After spending a total of 25 years at the club as a player and as a manager, this decision – taken together with the club – is one of the most difficult decisions I have ever had to make," Howe said in an open letter to fans. .
"However, although the affection and love I have for this football club always remains, collectively we feel that now is the right time for the club to take a new direction."
"Bournemouth will always be in my heart, but I firmly believe that now is the right time for the club to change."
Bournemouth had moved up from League Two to become an established Premier League team under Howe, who guided them to three promotions in six seasons.
But they lost 22 of their 38 games and finished 18th on the table, a safety point, and return to the Championship after five seasons in the Premier League.
Several big-money signings didn't work for Cherries the way Howe – who has played more than 250 times at the club – would have expected.
Extreme Jordon Ibe, who costs £ 15m from Liverpool in 2016, he played only two league games in 2019-20, and striker Dominic Solanke – who reached a £ 19m deal of the Anfield club in 2019 – achieved three league goals in 32 games.
The south coast club also suffered injuries, in addition to an experienced defender Charlie Daniels being dropped for the season in August 2019 and promising tip David Brooks demanding two operations who saw him lose most of the campaign.
Cherries Chief Executive Neill Blake said Howe was a Bournemouth legend who helped "transform the club's identity and history".
He said the decision to split from the company was "even more difficult, given our close personal friendship".
& # 39; What he achieved is a miracle & # 39;
Former Bournemouth boss Harry Redknapp, who ran the club from 1983 to 1992 and took him to the second division of English football for the first time in its history in 1987, predicts Howe will be "back in the Premier League soon".
He told BBC Radio 5 Live: "I am very surprised. I was sure that he would look to recover the club next season. The work he did was incredible.
"He took a club that was fighting in the third echelon for the championship – which was a miracle – and then for the Premier, which I thought was impossible to do."
"So for five years, he made us play incredible football, defeating everyone at different times – it was incredible.
"The stadium has only 11,000 people, they had no right to enter the Premier League. For 100 years, they have never been out of division three or four. No disrespect, but it would be like Rochdale, or clubs like that, joining the Premier League. It has been incredible.
"It won't be an easy job to follow him. He couldn't do that anymore and he leaves with his head held high."
Howe's Timeline as Bournemouth Manager
December 31, 2008 – Howe, only 31, takes on the responsibility of the janitor for club 91 in the American Football League and faces demotion and possible liquidation. Despite starting the season with -17 points, Cherries remain on the last day of the season after winning the last three games.
May 8, 2010 – Bournemouth are promoted to League One in Howe's first full season as permanent boss, finishing second on 83 points.
January 14, 2011 – In his first season in League One, Howe takes the Cherries to the recap and is courted by Championship clubs. He finally leaves for Burnley. Bournemouth lose on penalties to Huddersfield in the play-off semifinals.
October 16, 2012 – After 18 months without notable success at Turf Moor, Howe returns to Bournemouth. They are promoted to the championship behind Doncaster. It is the second time in the club's history that he has played in the first two levels.
May 2, 2015 – After finishing 10th in his first season in the championship, Howe leads the cherries to the title, beating Watford on the last day. The season includes an 8-0 victory in Birmingham and promotion to the top echelon is the first time the club has performed.
May 17, 2016 – Bournemouth survive by a five-point lead after an inaugural Premier League season, in which they spend £ 10 million on Benik Afobe and beat Chelsea and Manchester United.
May 21, 2017 – Bournemouth finish ninth in the first division, with Joshua King scoring 16 goals in the Premier League.
May 13, 2018 – In the relegation zone at Christmas, Howe projects an impressive recovery and Bournemouth finishes in 12th place.
12 May 2019 – Bournemouth reach sixth place in early December, but in the second half of the season they finish 14 to 11 points, without problems.
January 1, 2020 – A 4-0 loss at West Ham causes Bournemouth to fall into the relegation zone for the first time in 2019-20.
July 26, 2020 – Bournemouth's five-year Premier League stay ends despite winning Everton because Aston Villa secured a draw at West Ham.
August 1, 2020 – Howe leaves the club by mutual consent.