"I am very happy for him to win the Championship but more to retire. I had a chat with him and I think he made the right decision.
"He doubted to stay or not, but I told him 'leave in a perfect physical conditions because you never know what can happen. You have a wonderful life. You have money, everything. 41 years old is the right time to stop.'"
Rossi and Biaggi had sparred verbally as Rossi, eight years younger than Biaggi, worked his way up through the ranks, finally meeting head-to-head when Rossi joined the premier 500cc class in 2000.
Both won two races - Rossi for Honda, Biaggi for Yamaha - that year, but were beaten to the title by Kenny Roberts
The 2001 season was then dominated by the Rossi-Biaggi rivalry, with the gloves-off from round one - where Biaggi elbowed Rossi onto the grass along the straight-finish straight at Suzuka, for which he received a 'one fingered wave' from the #46 on his way to victory.
The pair later scuffled, behind closed doors, prior to the podium ceremony for round six at Catalunya
, prompting a further warning from the FIM.
But the intense competition between the two Italians, combined with their contrasting stereotypes - Rossi the gifted, carefree youngster, famous for exuberant post-race celebrations and Biaggi the brooding 'Dark Knight' perfectionist - undoubtedly took MotoGP to new heights of popularity.
On paper, Biaggi and Yamaha were never able to mount a sustained title challenge to Rossi and Honda. Rossi broke free of Biaggi after nine rounds of the 2001 season, then dominated the start of the four-stroke MotoGP era.
After finishing runner-up to Rossi in 2001 and 2002, Biaggi switched to the satellite Honda Pons team for 2003 and 2004, the year Rossi made his victorious switch to a heavily redesigned Yamaha M1.
By then relations between Rossi had Biaggi had improved, largely due to Gibernau (Gresini Honda) replacing Biaggi as Rossi's closest competitor.