Gregore struck a late winner as Botafogo ended a 29-year wait by clinching the Brazilian Serie A title for a third time on Sunday with a 2-1 home victory over Sao Paulo.
Gregore capitalized on an errant defensive pass to drill home a low finish in the 92nd minute after Sao Paulo's William Gomes canceled out Jefferson Savarino's opener.
The result at Rio de Janeiro's Olympic Stadium meant Botafogo finished the season with 79 points, six points ahead of second-placed Palmeiras.
It was the second major trophy for Botafogo in eight days after the Rio outfit beat Atletico Mineiro 3-1 in the Copa Libertadores final in Buenos Aires.
Botafogo manager Artur Jorge said the titles marked a redemption of sorts after the heartbreak of last season, when the team squandered a 13-point lead to lose the Serie A title to Palmeiras.
"I'm very happy, not just because we've achieved our objectives this season, but because of what the players went through last year," Jorge, who joined the club in April from Portugal's Braga, told Sportv.
"We had an extraordinary season and the fans deserve this more than anyone. They have suffered a lot to get to this point."
Botafogo, whose previous top-flight titles came in 1968 and 1995, is only the third club to secure the Brazilian Serie A and Copa Libertadores titles in the same year. The feat was also achieved by Pele's Santos in 1962 and 1963, and Flamengo in 2019.
Jorge's men will now turn their attention to the inaugural edition of the FIFA Intercontinental Cup in Qatar, where they will meet Mexico's Pachuca in the quarterfinals on Wednesday.