Watford are set to receive £225,000 after former winger Will Buckley joined Sunderland from Brighton and Hove Albion.
Buckley has joined the Black Cats for a reported £2.5m fee which would net the Hornets £225,000.
The 24-year-old spent three seasons with Brighton after he left Watford in 2011 in a £1m move.
When the winger, who made 43 appearances for the Hornets in a two-year spell, departed from Vicarage Road the club negotiated a 15 per cent sell-on clause on any transfer over the £1m fee.
Buckley has signed a three-year deal at the Stadium of Light and is reunited with former Seagulls boss Gus Poyet.
It's the second time this summer the Hornets have netted a cash windfall from the sale of one of their former players.
Last week Britt Assombalonga completed a move to Nottingham Forest with the fee believed to be £5.5 million.
If that figure is correct, Watford were due £2.15m from Peterborough in addition to the £1.2m the Golden Boys initially received for the young striker.