Barcelona have reached an agreement with Watford to sell Gerard Deulofeu to the Premier League club for an initial fee of €13 million, the La Liga side confirmed on Monday.
Barcelona may also receive an additional €4m in performance-related add-ons, while they are due a percentage of any future sale, too.
Deulofeu, 24, joined Watford on loan in January and despite missing a number of games through injury had made it clear he was keen to return to Vicarage Road on a permanent basis
The Spain winger only re-joined Barca last summer in a €12m deal from Everton but he found minutes hard to come by under coach Ernesto Valverde.
After making 17 appearances, Ousmane Dembele's return from injury and the signing of Philippe Coutinho in January pushed him further down the pecking order.
A six-month loan move to Watford followed, where he scored one goal in seven appearances for Javi Gracia's side.
Deulofeu came through the academy at Barcelona and was widely expected to be a future first-team star but things never quite worked out for him at Camp Nou.
Following loan spells with Everton and Sevilla, he made a permanent move to Goodison Park in 2014.
However, he fell out of favour under Ronald Koeman, which saw him join AC Milan on loan in 2017, where his form over six months tempted Barca into re-signing him from Everton last summer.
Back home, though, he was unable to recreate his San Siro form and he now leaves Barca for England for the second time in his career, signing a five-year deal at Vicarage Road.