Alex Volkanovski was literally holding his adorable newborn Reign when he got the call -- Charles Oliveira was out and Islam Makhachev needed an opponent -- and the 145 lb. champ almost instantly knew it was time for daddy to go to work!
Volkanovski joined Michael Babcock on the "TMZ Sports" TV show (airs daily on FS1) on Wednesday ... where Alex "The Great" talked about the phone call he received late last week from his manager.
"I think I might've had Reign, my newest addition to my family, my newborn Reign," Alex said .