Anthony Joshua has revealed who he believes is the greatest heavyweight champion of all time - and it is not Muhammad Ali, which would come as a surprise to many. 

In fact, the 28-year-old has cited Jack Johnson as his favorite and has admitted to watching documentaries on YouTube in preparation for his crucial upcoming unification clash with Joseph Parker. 

Johnson was the first African-American world heavyweight champion, with his reign lasting from 1908 to 1915, having beaten Tommy Burns for his first title in 1908. 

Joshua has been taking tips and inspiration from the "Galveston Giant" and continues to study the sport in order to improve. 

He also mentions Alabama native Evander Holyfield as the boxer from whom he has "learned the most."

Holyfield competed from 1984 to 2011, and is the only boxer in history to hold the undisputed title in both cruiserweight and heavyweight divisions, earning the nickname "The Real Deal" as a result. 

“At the minute I’m obsessed with documentaries. YouTube is my new friend,” Joshua said

“I think the greatest heavyweight of all time is Jack Johnson, but the heavyweight I learned the most from was Evander Holyfield.

“When you look at it, a lot of them left the game in a bad way.”

Johnson boasted a record of 73 wins, 10 draws, and 13 losses, which is an impressive tally for his era.

Before his first heavyweight title win, African-American fighters were not allowed to challenge for the highest prizes in the sport. 

During the fight against Burns, police intervened in round 14, with Johnson being declared the winner as a result. 

After enjoying a reign spanning seven years, the man from Texas finally lost his crown to Jess Willard during a 45-round match. 

Joshua has plenty of inspiration to draw upon and will be looking to channel every bit of it during his match with Parker on March 31 at the Principality Stadium in Cardiff.