Since then, he has made guest appearances in Season 4's "The Perfect Pieces in the Purple Pond" and "The End in the Beginning" (dream sequence), Season 5's "The Parts in the Sum of the Whole" (flashback) and returned in the Season 11 finale "The Nightmare within the Nightmare", and had a recurring role in the series' ...

What episode does Zack Addy come back?

Zack also returns as a guest star in the season 5 episode The Parts in the Sum of the Whole.

Why did Zack Addy leave bones in season 3?

Eric Millegan did not leave Bones because of his bipolar disorder. ... He explained that he had a tough time dealing with depression and mania while shooting the first season of Bones, partly triggered by moving from New York to LA for the series.