Cliff Williams

Bassist said health issue caused him to retire after the conclusion of band's 'Rock or Bust' tour.

Three members who left the band at various points during the 'Rock or Bust' tour have returned.

Whatever the band was doing in the city last year, it appears the retired bassist was there for at least part of it.

Guitarist Angus Young offered a special tour-ending salute to bassist Cliff Williams, who is retiring from AC/DC.

Cliff Williams will play his last concert with AC/DC in Philadelphia on Sept. 20, 2016.

His departure leaves Chris Slade – who had an earlier stint from 1989-94 – as the most veteran member of AC/DC after Angus Young.