Ray Lewington has been sacked as Watford boss after a disastrous run of results, the club confirmed on Tuesday.
Lewington took over from Gianluca Vialli in July 2002
The Hornets are only four points clear of the Championship relegation zone after picking up just four wins in the past 24 league matches.
Former Crystal Palace boss Lewington took over from Gianluca Vialli in July 2002 and steered the Hornets to the Carling Cup semi-finals this season.
Nigel Gibbs and Terry Bullivant have taken over on a temporary basis.
Watford chairman Graham Simpson thanked Lewington for his work at the club.
"It has been a great pleasure working with him because he is a genuinely honest man who brings great integrity to his work," he told the Hornets' website.
"Ray will also be remembered at Vicarage Road for taking Watford to two major cup semi-finals in three seasons.
"However, we have recently seen a slump in form at a key point in our season with just one point being gained from our last four home matches in the Championship."
Simpson said the club hoped to have a new boss in place before the next league fixture at Burnley on 2 April.
In their statement to the Stock Exchange on Tuesday, the club said: "Watford Leisure announces that Watford first team manager, Ray Lewington, has been relieved of his duties with immediate effect."