Etienne Capoue has left Watford after the midfielder completed a permanent move to Spanish side Villarreal for an undisclosed fee.
The Frenchman looked set to join former Hornets boss Javi Gracia at Valencia in the summer, but a transfer failed to materialise.
The 32-year-old played 181 games for the Hornets after joining from Tottenham in 2015, for a fee of around £6.3 million, which was a club record at the time.
A statement from Watford confirmed his departure.
'Etienne Capoue has left Watford after completing a permanent transfer to Spanish La Liga side Villarreal for an undisclosed fee.
'The Hornets thank Etienne for his efforts over the past five-and-a-half years and wish him well for the future.'
The club also released a tribute video with his best highlights from his time in Hertfordshire, with the caption: 'Merci Etienne'.
The Frenchman clocked up 11 appearances for Watford this season, his final outing for the Hornets was their 1-0 win over Championship leaders Norwich City on Boxing Day.
He scored 14 goals during his time at Vicarage Road and was named player of the season at the end of the 2018/19 campaign.
The Hornets finished 11th that season and also reached the FA Cup final, losing 6-0 to Manchester City at Wembley.
Capoue first arrived in England when he joined Spurs from French side Toulouse for £10million in 2013.
The Frenchman will link up with former Arsenal manager Unai Emery at the Spanish club and is set to deputise for the injured Vincente Iborra.
The Spanish midfielder will miss the rest of the season after rupturing his anterior cruciate ligament against Real Betis earlier in December.
Emery is rebuilding his reputation after being sacked by the north London club in 2019 and has guided to Villarreal to fifth in La Liga, five points behind leaders Atletico Madrid.
Next up for Emery's side is a home game against Levante on Saturday.