McGregor, who ranked as Forbes' highest-paid athlete in any sport in 2021, is a controversial figure and one of the biggest names of mixed martial arts (MMA).

He has not competed in UFC for more than two years because of injury, but hopes to return against Michael Chandler of the United States at the end of the year or start of 2024.

McGregor took part in a jiu-jitsu class with coach John Kavanagh, and was promoted to black belt after 20 years practicing the discipline.

"Thank you John for everything over the years, and to all of my team mates throughout this incredible jiu jitsu journey," he wrote on Instagram.

"Thank you all so much from the bottom of my heart.

"A Brazilian jiu-jitsu black belt, wow!

"Praise be to God and then Helio."

Brazilian jiu-jitsu is a self-defence martial art focused on grappling, ground fighting and submission holds.

Its skills and techniques are key for MMA.