Former Inter Milan coach Luigi Simoni, who led the club to the UEFA Cup title in 1998 during the era of Brazilian star Ronaldo, died in Pisa on Friday at the age of 81 years.
"Today, 22 May, he left us. Not just any date, the most Inter-related date of all," Inter Milan said in a statement.
Inter on Friday marked the 10th anniversary of winning the Champions League under Jose Mourinho, becoming the first Italian team to win the treble.
Simoni, whose coaching career spanned four decades and 17 different Italian clubs, never recovered after suffering from a stroke almost a year ago.
"Gigi Simoni was not just a coach for me," said Ronaldo on Instagram.
"If I think of him today, I think of a wise and good man who did not order you to do things, but explained why those things were important. I think of a teacher.
"He was the conductor; we the orchestra."
"A great football man has left us," added Italian football federation president Gabriele Gravina.
A midfielder during his playing career, Simoni played 368 times, including 187 in Serie A, scoring 32 goals for clubs including Juventus, Torino and Napoli, with whom he won the Italian Cup in 1962.
He started his coaching career at former club Genoa in 1974, guiding them to Serie A the following season, the first of eight promotions achieved for his teams.
He was most remembered for his time with Inter Milan, joining along with Ronaldo in 1997, and lifting the UEFA Cup the following year after beating Lazio in the all-Italian final.
They missed out on the Serie A title that season, finishing second to Juventus.
"He arrived in the Nerazzurri dugout in 1997, together with 'El Fenomeno', Ronaldo," Inter Milan recalled.
"That combination, Simoni-Ronaldo, will remain in everyone's hearts forever, and not just those of Inter fans.
"That was a father-son relationship, one in which he showed great compassion towards a truly special footballer: Simoni loved to tell us, 'I learned more from him than he did from me that season.' A phrase that brilliantly encapsulates what type of person he was."
Two-time World Cup winner Ronaldo, 43, added: "Thanks mister, you taught me more than you imagine."
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Gigi Simoni per me non è stato solo un allenatore. Se oggi penso a lui, penso a un uomo saggio e buono, che non ti ordinava di fare le cose, ma ti spiegava perché quelle cose erano importanti. Penso a un maestro, come in quella foto che facemmo a Natale: lui direttore, noi l’orchestra. Lo ricordo così, con quel sorriso, la sua voce sempre calma, i suoi consigli preziosi. Potevamo e dovevamo vincere di più, ma abbiamo vinto insieme, la cosa che ci raccomandava sempre: grazie mister, mi hai insegnato più di quanto immagini