AEW star PAC is dead at 40 ... stunning news that comes less than a day after he wrestled and appeared throughout the company's biggest show of the weekend.

All Elite Wrestling announced PAC's death Sunday night, remembering the British wrestler -- real name Benjamin Satterley -- for his innovative high-flying moves and incredible in-ring ability.

PAC competed Saturday at AEW's All Out pay-per-view in Chicago, challenging Andrade El Idolo for the AEW National Championship.

He lost the match and shook Andrade's hand afterward ... but that wasn't PAC's final appearance of the night.

PAC later returned during the main event ... getting involved in the AEW World Championship match between fellow Death Riders member Jon Moxley and Will Ospreay.

AEW did not reveal a cause of death or any other details surrounding his passing.

The Newcastle, England native began wrestling in 2004 and joined AEW in 2019 ... becoming the inaugural AEW All-Atlantic Champion and a two-time AEW World Trios Champion.

Before AEW, Satterley competed in WWE as Neville ... winning the NXT Championship and becoming a two-time WWE Cruiserweight Champion.

RIP