Slaven Bilic was appointed as the new manager byWatford.
Bilic will take charge of just 11 matches during his 18-month contract at the helm of the Hornets.
The change to be in the best interests of the club was stated by the owner in a statement.
Rob had enough time to show us the identity of his team but performances haven't reflected our hopes and ambitions.
We have secured the services of an experienced coach who has recently been promoted to the top flight in England.
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After Forest Green won the League Two title, he was brought in by the club to help them get back into the top flight.
The 39-year-old made a promising start as the Hornets collected seven points from their first three games but, after managing just one more win, he became the 17th permanent manager to lose his job.
A former Croatia international player and head coach, Bilic takes over with a 10th place in the Championship and a trip to the Britannia Stadium to take on the Potters.
In his most recent work in English football, the 54-year-old guided West Bromwich to promotion from the Championship.
"Bilic's other staff will be confirmed in due course," the statement concluded.