Italian Felice Gimondi, one of only seven riders to have won all three Grand Tours, has died at the age of 76 after suffering a heart attack while swimming in Sicily on Friday.
"A great champion who made our sport more human has left us, a great man," the Italian Cycling Federation said in a statement.
Gimondi won the 1965 Tour de France in his first season as a professional, aged 22.
He won the Giro d'Italia two years later and the Vuelta a Espana in 1968.
Gimondi also won the Giro in 1969 and 1976 to take his Grand Tours tally to five before retiring in 1978.