Watford announced the return of Quique Sanchez Flores as head coach on Saturday after Javi Gracia was sacked following a poor start to the season.
The Premier League club announced the changes in two separate statements published within minutes of each other on social media.
Flores was previously in charge of the club, who are currently bottom of the Premier League with one point after four matches, during the 2015-16 season, after which he was surprisingly sacked.
He is one of the 10 managers, including Gracia, who have left Watford in the last seven years.
Flores quit Chinese club Shanghai Shenhua last month, citing personal reasons.
Gracia departs after 20 months in charge at Vicarage Road. Chairman and CEO Scott Duxbury said: “Javi has represented Watford with great dignity and will always be deserving of our fullest respect for his achievements.
“Javi Gracia’s staff will also be leaving the club, ahead of the imminent appointment of a new coaching team.
“Everyone at the Hornets wishes Javi and his staff all the very best for the future, and they will always be welcome visitors in the future at Vicarage Road.”
Watford have appeared to be in a tailspin since the end of last season when they were humiliated 6-0 by Manchester City in the FA Cup final.
But even before that game there were concerns, with three defeats in the previous four games, and the club have not won since April 20, when they were seventh in the Premier League.
The start to this season contrasted strongly with the beginning of the 2018-19 campaign when they won there first four league games.
An opening-day home defeat to Brighton & Hove Albion was followed by further losses at Everton and home to West Ham United, with the club finally scraping a point in last Saturday’s 1-1 draw at Newcastle United.