Sir Elton John described Graham Taylor as "like a brother to me" following the former England manager's death at 72.
Sir Elton appointed Taylor as Watford manager in 1977, a year after the singer took ownership of the club.
Within five years, Taylor took the Hornets from the old Fourth Division to runners-up in the top flight, going on to reach the 1984 FA Cup final.
"We will cherish Graham and drown our sorrows in the brilliant memories he gave us," Sir Elton wrote on Instagram.
He added: "This is a sad and dark day for Watford.