Mariano has competed on four seasons of the hit series -- and came out victorious at the end of Survivor: Redemption Island in 2011 -- while Diaz-Twine has competed in three seasons and returned home the Sole Survivor twice.
For this upcoming season, Mariano and Diaz-Twine won't be angling for another win, but instead are part of the season's twist.
As 20 Survivor hopefuls scheme, play, manipulate and scavenge in an effort to stay in the game -- this season being played on Fiji's Mamanuca Islands chain -- the struggling contestants will also be fighting for the chance to get advice and guidance from two of the most successful contestants in the show's history.
Speaking with The Hollywood Reporter, Mariano explained that he initially had no interest in coming back to do another season of the grueling show, after already having spent a combined total of 117 days marooned in exotic locales for the chance at a big cash prize.
"I always said I wouldn't come back to Survivor unless it was some kind of unique experience that made sense," he shared. "When Jeff pitched us the idea of us coming back as coaches or mentors, it rang true."
The 43-year-old Boston native and fan-favorite said that he and Diaz-Twine will be running something of a "Survivor boot-camp" on their little section of the eponymous Island of the Idols, and plan to teach the newcomers tips and tricks that will help them thrive -- like catching fish and starting fires.
However, he said that they will likely be teaching them a lot more about "strategy questions and game theory and numbers" as the season progresses -- considering Survivor is as much about surviving the elements as it is about surviving the machinations of your fellow competitors.
Survivor: Island of the Idols premieres this fall.