The manager has been placed on 'gardening leave', meaning that he cannot work for anyone else.
"Hull City AFC confirms that Phil Brown has been relieved of his managerial duties at the club and has been placed on gardening leave with immediate effect," chairman Adam Pearson told City's official website.
"Brian Horton and Steve Parkin will take charge of first-team duties until further notice.
"We would like to place on record our sincere thanks to Phil for the major success achieved during a period of four seasons in charge at the club and wish him every success for the future.
"Promotion to the Premier League in 2008 and retention of our status on the last day of the 2009 season are unique events in the history of Hull City AFC and both were achieved under Phil's stewardship during a period which will never be forgotten by all connected with the club."
City succukmbed to a late winner at home to Arsenal on Saturday after it looked like they had done enough to secure a valuable point.
With their Premier League status in doubt, it is clear that the Tigers hierarchy felt that the time had come to act.
"However, retention of Premier League status is paramount and the board believes that a change in managerial direction is the correct option at this time," Pearson added.
"The club will keep supporters completely up-to-date in respect of any managerial appointment but, in the meantime, Brian Horton and Steve Parkin will prepare the team for our important game at Portsmouth next Saturday."
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