The late, great, Muhammad Ali is known to be the greatest of all time in the boxing ring but a lesser known fact is that the pugilist was also an artist. A rare piece of artwork has now sold for $1 million.

According  to CBS News, on Oct. 5, 28 pieces of his artwork, titled the "Who Knew?" collection, were put up for auction and sold for  $945,524.

Helen Hall, who works with the auction house that sold the collection, told CBS News, "I think the thing about these works is the subject matter are all things that were close to his heart. He'd draw his boxing matches and he references Islam, references race riots that happened in the '60s. So they're personal works — which makes them so — well, when I first opened the box and saw them in the flesh I got goosebumps." 

The auction house revealed Ali learned to paint from his father, Cassius Clay Sr. and he took lessons from artist LeRoy Neiman. According to Ali’s longtime friend Rodney Hilton Brown, who inspired him to explore art even more, the boxing  legend said about his artwork, “I paint pictures with meanings.”

Muhammad Ali is a former World Heavyweight champion who became a leading voice for civil righrs in the 1960s and '70s. Born Cassius Clay, he changed his name in 1964 when he joined the Nation of Islam.

Ali died in 2016 at 74 years old. 

See some of the artwork below: