Watford have confirmed the sale of Dodi Lukebakio to Hertha Berlin for a fee Sky Sports News understands is in excess of £18m.
The 21-year-old forward joined Watford from Belgian side Anderlecht in January 2018 but only managed 15 minutes of action during his time with the Hornets.
Lukebakio spent last season on loan in the Bundesliga with Fortuna Dusseldorf, scoring 14 goals in 34 appearances in all competitions, including a hat-trick against champions Bayern Munich.
The Belgium international returns to Germany with Hertha, who finished 11th last season, one place below Fortuna.
Hertha Berlin signed Dutch youngster Daishawn Redan from Chelsea last week.