Cliff Williams

We're rockin' around the Christmas tree and into a long list of rock stars who are celebrating their birthdays this month.

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.

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.