Muhammad Ali and Joe Frazier may have been adversaries in and out of the boxing ring, but the two also shared a mutual admiration for each other.

Ali, who is known as the Greatest largely because of his three history-making bouts with Frazier, will pay his respects to his rival when he flies to Philadelphia to attend Frazier’s funeral on Monday, according to the Associated Press.

Frazier died Monday night after a brief bout with liver cancer. He was 67.

Frazier and Ali will forever be linked due their intense rivalry during the 1970s with Frazier becoming the first man to defeat Ali in 1971. Ali would go on to win the next two fights in their trilogy.

Their rivalry is remembered as much for thrilling moments in the ring as they are for the insults Ali aimed at Frazier, calling him a gorilla and an Uncle Tom.

Though Frazier continued to harbor resentment toward Ali for decades, the two great heavyweight champions had made amends in later years, as Ali suffered from Parkinson’s disease.

"This will be an opportunity for his many fans, supporters and boxing lovers from around the world to pay their final respects to Joe Frazier," his family said in a release.

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(Photo: Hannah Foslien/Getty Images for Starkey Hearing Foundation)