The Nigerian international will join for up to £20 million. Dennis scored ten goals and assisted six more for the Hornets in the Premier League last season, but it was not enough to keep them up.
The 24-year-old will be hoping his new club can manage to stay in the top flight.
Born in Yola, Nigeria, in 1997, Dennis started his youth career in his homeland with the Kwara Football Academy. He joined in 2012 before moving to Ukraine to sign for top-flight side Zorya Luhansk in 2016.
He scored six goals in 26 appearances and gained Europa League experience after facing Feyenoord, Manchester United, and Fenerbache.
His form in Ukraine caught the attention of Belgian side Club Brugge. The Brussels club confirmed the signing of Dennis in May 2017 on a four-year contract. After notching two goals on his debut, the Nigerian netted four goals in his first three Jupiler Pro League appearances.
Featuring 116 times across all competitions for Club Brugge, Dennis showed he could perform at the highest level after scoring two goals in the 2019 Champions League group stages against Real Madrid at the Santiago Bernabeu as the Belgium side earned a 2-2 draw.
Dennis made 24 European appearances in total for Club Brugge and moved to a new challenge in the Bundesliga with FC Koln in 2021, appearing ten times during a loan spell. The forward then signed a five-year contract with Watford.
He became the club’s 13th signing of the summer, and number 14 followed immediately
Cheikhou Kouyate checks in for Nottingham Forest
Nottingham Forest later confirmed the signing of experienced midfielder and free agent Cheikhou Kouyate on a two-year contract.
The Senegalese international was released by Crystal Palace after last season. The 32-year-old played 31 times for the Eagles during the campaign. He joined the club from West Ham in 2018.
Kouyate made 141 appearances for the South London club.
Kouyate has won 82 international caps for Senegal and was part of the squad that lifted the Africa Cup of Nations title last year.