Four former UFC fighters, including a trio of former UFC title challengers, are going from the MMA world to the world of bare-knuckle fighting.

During the BKFC Champions Summit press conference with Conor McGregor, held at the Hard Rock Hotel in Las Vegas ahead of BKFC 48, McGregor announced the additions of Yoel Romero, Thiago Santos, Derek Brunson, and Aspen Ladd to the BKFC roster.

Romero and Santos were the particular focuses of the announcement -- highlighting their striking power and their veteran statuses.

BKFC Announces Four Signings, Including Yoel Romero And Thiago Santos

Romero and Santos, in fact, faced off in MMA just a year-and-a-half ago. The two faced off during the PFL vs. Bellator broadcast, with Romero, who was representing Bellator, winning via a clear unanimous decision.

Romero has not fought in MMA since the win, while Santos had one more fight, a short-notice loss to eventual 2024 PFL heavyweight champion Denis Goltsov during the regular season.

Romero -- a freestyle wrestling silver medalist at the 2000 Olympics and a former freestyle wrestling World and Pan-American champion -- went 16-7 in professional MMA, including a 9-4 UFC record. Romero scored victories over the likes of Lyoto Machida, Ronaldo "Jacare" Souza, and Chris Weidman, but was unsuccessful in middleweight title challenges of Robert Whittaker and Israel Adesanya.

Romero then had a five-fight stint in Bellator, going 3-2 -- which included the win over Santos and an unsuccessful title shot against then-Bellator light heavyweight champion Vadim Nemkov.

Santos fought in the UFC for about a decade, but his biggest stretch came when he jumped from middleweight to light heavyweight. Santos would finish Eryk Anders, Jimi Manuwa, and Jan Blachowicz, receiving a title shot against then-champ Jon Jones at UFC 239. Santos would lose in a controversial decision. That would be the start of a downward stretch Santos never recovered from, losing all but one of his fights since the Jones loss.

After his tenure with the UFC, Santos fought in the PFL, debuting with a loss to Rob Wilkinson -- a bout that would be overturned to a no contest.

Brunson came into the UFC as Strikeforce was being merged with the promotion and slowly being folded. Brunson earned victories over the likes of Lorenz Larkin, Uriah Hall, Lyoto Machida, and Kevin Holland, as well as losses to Souza, Whittaker, Adesanya, Anderson Silva, Jared Cannonier, and Dricus Du Plessis. Brunson fought in MMA once after his UFC days -- a win over Ray Cooper III at the 2023 PFL World Championships.

Ladd debuted in Invicta in 2015 and went unbeaten in five fights before joining the UFC two years later. Ladd won her first three UFC bouts before a loss to Germaine de Randamie. Ladd would struggle with consistent success -- and had a near-two-year period of inactivity at one point -- before parting ways with the UFC after a 2022 loss to Raquel Pennington.

Ladd debuted in PFL in November of that year with a win over former Bellator champion Julia Budd. She then competed in the 2023 women's featherweight season, losing to Olena Kolesnyk but defeating Karolina Sobek. Ladd missed the playoffs but fought in a showcase bout later that year, losing to current UFC women's bantamweight champion Kayla Harrison.

Ladd's last MMA fight came at the Bellator Champions Series event in Paris in May 2024, defeating Ekaterina Shakalova.