UFC president Dana White confirmed the news to MMA journalist Luke Thomas on Thursday. The highly ranked 155-pound fighters will square off at the end of the show, on a date to be determined.
Gaethje (18-0) is coming off a spectacular promotional debut on July 7 in Las Vegas. A former WSOF champion, Gaethje is known for his action-packed fighting style and delivered a Fight of the Year candidate in a TKO win against Michael Johnson.
Fighting out of Denver, Gaethje is a former collegiate wrestler at the University of Northern Colorado, but 15 of his professional wins have come via knockout.
Alvarez (28-5) is coming off a no-contest against Dustin Poirier at UFC 211 in May. That contest was also shaping up as a Fight of the Year contender, until Alvarez landed several illegal knees that stopped the bout in the second round.
Referee Herb Dean ruled the illegal knees as accidental, which resulted in a no-contest. Prior to that bout, Alvarez lost his 155-pound title to Conor McGregor in November, via second-round TKO. He fights out of Philadelphia.
Poirier (21-5) is the odd man out in this announcement. The 28-year-old is 5-1 since moving up from the featherweight division in 2015 and had been campaigning for a rematch with Alvarez, due to the controversial result.
The 26th season of TUF will feature 125-pound female flyweights, which is a new weight class in the UFC. The show will crown the division's inaugural champion in its season finale.