Watford have signed Ivory Coast striker Vakoun Bayo on a five-year deal from Belgian side RSC Charleroi.
He began his career in Tunisia in 2015 before moving to play in Slovakia.
He moved to Celtic in 2018 but only made two starts and 15 substitute appearances for the Scottish Premiership side, scoring four goals.
A move to Toulouse followed before arriving in Belgium at the start of last season, playing for Gent and then Charleroi.
Rob Edwards' Watford begin their Championship campaign at home to Sheffield United on 1 August.