At the time, the three-time World Heavyweight Champion took to Twitter to pay tribute to the Purple One, who died from an accidental Fentanyl overdose on April 21 at the age of 57, with a heartwarming message and throwback picture of the two hugging.
"We've lost a true original," Ali tweeted on April 22. "@Prince was someone who cared for others & used his genius to help many. #AliTweet."
The picture, which was retweeted by many fans and celebrities, including Holly Robinson Peete, was taken in 1997 at a press conference promoting The World Hearing Honors, a benefit concert promoting international harmony and tolerance. When Prince took the stage to deliver a speech at the event, he had nothing but kind, admirable words to share about the boxing icon.
Prince and Ali. 💔💔💔💔💔💔💔💔 pic.twitter.com/TwZIwQ0qgI— Holly Robinson Peete (@hollyrpeete) June 4, 2016
"My friend called me a couple of days ago and asked me. He said, 'Muhammad wants you to -- and I said 'Yes,'" the legendary musician explained to reporters. "I didn't even let him finish. He could have said, 'Mow the lawn,' and I would have been down with it. Muhammad's my hero. He has been since I was a child. As you can see, he's such an inspiration to many people."
Prior to his death, Ali was quite vocal on Twitter, often posting photos from his time in the ring and positive and inspiring messages to his 810K followers. He would also send kind notes to his friends and fellow icons, including recent birthday wishes to both U2's Bono and Dwayne "The Rock" Johnson.
He also congratulated Kobe Bryant on his retirement from the NBA after a 20-year-career in April, writing, "Congrats @KobeBryant on an amazing career. One of the greatest to ever play the game! #ThankYouKobe."
As ET previously reported, Ali's final boxing retirement came in 1981 after losing several high-profile fights, including a particularly violent defeat to Larry Holmes. Several years later, he received a formal Parkinson's diagnosis. Though he was slowed by his illness, he remained indefatigable.
Since news broke, athletes, entertainers and other celebrities have been paying their respects to Ali on social media. Hear some of their touching tributes in the video below.