After regaining his WBC title with a technical knockout victory against Tony Harrison in 2019,[2] Charlo unified the light middleweight division with a knockout victory against WBA (Super) and IBF champion Jeison Rosario in 2020, picking up the vacant Ring magazine title in the process.

[3] Following the win, reigning WBO champion Patrick Teixeira expressed a desire to face Charlo in a fight for the undisputed championship.

However, Teixeira had to fulfill his obligation to face the WBO's mandatory challenger, former WBA (Regular) champion, Brian Castaño.

[7] The fight ended in a draw (tie) after twelve rounds, allowing both champions to retain their titles.

A rematch was fought on May 15, 2022, when Charlo defeated Castano by a tenth round technical knockout to unify the championships.