Thornton, 41, is now skating with HC Davos in the Swiss National League in preparation of the 2020-21 NHL season.
Thornton was originally drafted from the Soo Greyhounds (OHL) by the Boston Bruins with the first overall selection in the 1997 NHL Draft.
It looks like Marleau and Thornton have played their last game as teammates, but knowing how much they love to play hockey, don't put it past them to keep playing beyond the 2020-21 NHL season and join forces on the Sharks or another team.
He has recorded 1,509 points (420 goals, 1089 assists) in his career while adding 133 points (31 goals, 102 assists) in 179 playoff games.
Thornton's deal does not include a substantial number of performance bonuses.
Thornton's move north of the border stunned everyone, including Marleau, who similarly left the Sharks for the Leafs in 2017. He finished the season with 125 points in 81 games and took home the Art Ross Trophy as the league's leading scorer as well as the Hart Trophy.
The one thing missing in Joe Thornton's star-studded career is a Stanley Cup. But with 31 points last season, the playmaking center will have a depth role in Toronto.