It's been confirmed that Ralph Waite will return in season 7 of Bones as Booth's grandfather. We will also finally get to see a glimpse at Booth's estranged father via a flashback. The scene will revolve around the baseball stadium seats Booth moved into his apartment last season.
Ralph Waite will return in an episode that will feature three generations of Booth men. We'll actually see Booth's dad via an extremely emotional flashback to Booth's childhood.
Source: TV Guide