"Following four incredible seasons with the Tigers including two promotions and our first-ever FA Cup final, we can confirm manager Steve Bruce has left the club by mutual consent," City said in a statement on Friday.
"The board of directors would like to thank Steve for all his efforts since his appointment in 2012 culminating in a glorious day at Wembley in May which saw the club bounce back into the Premier League."
Hull, relegated in May 2015, made an immediate return to the top flight via a 1-0 victory over Sheffield Wednesday in the Championship promotion playoff final on May 28.
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The club were also beaten 3-2 by Arsenal in the 2014 FA Cup final at Wembley.
Hull said Bruce "will be remembered for being the most successful manager in our history".
The club added that assistant Mike Phelan would take charge as caretaker until a new manager was named.
Bruce was in contention to replace Roy Hodgson as England boss before the Football Association appointed Sam Allardyce on Friday.
According to the BBC, the 55-year-old Bruce had wanted assurances about his role with Hull who have put takeover talks on hold until September.
The club are suffering an injury crisis with only 13 fit players available before their league campaign begins with a home game against champions Leicester City on Aug. 13.
Former Manchester United defender Bruce has also managed Sheffield United, Huddersfield Town, Crystal Palace, Birmingham City, Sunderland and Wigan Athletic.
(Reporting by Toby Davis and Rex Gowar; editing by Ed Osmond and Tony Jimenez)
