"Little brother" Billy Crystal pays tribute to Muhammad Ali

Among those affected by the passing of boxing champion Muhammad Ali, many eyes fell to Billy Crystal, whose impression of the boxing legend is itself the stuff of legend.

An unlikely friendship formed between the pugilist and the prankster after Crystal, in his first television appearance, imitated both the boxer and the famous sports personality Howard Cosell at a special honoring Ali.

The now-iconic impression received its seal of approval that night Crystal wrote in a 2010 essay for USA Today: "He loved it and started calling me 'little brother,' the nickname he still uses for me to this day."

On Friday afternoon, when reports of Ali's worsening condition circulated the web, Crystal took to Twitter to pay homage to "the greatest man [he's] ever known," by sharing a video from his 1979 performance at Ali's retirement tribute at the Great Western Forum called "15 Rounds."

The piece serves as a quick, comedic retrospective of the champion's career with each round marked, in true boxing match form, by a bell. In short, it packs a sentimental punch.

On Friday, Crystal along with former President Bill Clinton and journalist Bryant Gumbel will deliver eulogies at Ali's funeral in his hometown of Louisville, Kentucky.