According to Sid's son, Gunnar, he died after a lengthy battle with cancer.

"He was a man of strength, kindness, and love, and his presence will be greatly missed," Gunnar said in a statement.

"We appreciate your thoughts and prayers as we grieve this loss."

Sid -- real name Sid Eudy -- was a staple for WWE and WCW ... winning world championships for both promotions numerous times.

Sid kickstarted his professional wrestling career in the late '80s ... and went on to have iconic matches -- including headlining WrestleMania VIII at WrestleMania XI.

Sid had epic rivalries with fellow legends like Ric Flair, Hulk Hogan, the Undertaker and Sting during his time in the ring ... just to name a few.

Sid wrestled under a number of names throughout his career ... also famously going by Sycho Sid and Sid Justice.

He had his final match against Paul Rosenberg in August 2017 ... as part of Great North Wrestling.

Sid dealt with a handful of injuries during his career ... including a leg injury during a WCW Pay-Per-View event in 2001, as well as shoulder, back and knee issues.

Ric Flair shared his condolences on social media ... saying, "So Sorry To Hear Of The Passing Of Sid Justice. For All Of You Out There That Have Known That We Hadn’t Gotten Along In Business -- The Last Time I Saw Him, We Hugged, He Called Me Champ, And I Said Thank You!"

"He Has A Beautiful Family, And His Family Should Know That He Was Much More Than A Softball Player. A Man. Period. Rest In Peace!"

Sid is survived by his two sons, Frank and Gunnar, and his wife, Sabrina Paige.