The professional boxer, who held the WBO ligh-middleweight from 2015-2016, has a younger brother who is also a professional boxer; what is this brother's name?
Liam Smith (boxer): Liam Smith (born 27 July 1988) is a British professional boxer. Callum Smith: Callum Smith (born 23 April 1990) is a British professional boxer who competes in the super-middleweight division, and held the European, the British, and the WBC Silver titles between 2015 and 2017. Callum Smith:  He is the youngest of the Smith brothers—Paul, Stephen, and Liam—all of whom are professional boxers.
i don't know