In ETonline's exclusive look at the upcoming episode, Groban uncovers the secret double life led by Zimmerman -- his grandfather, eight generations removed -- in the 1680s.
At the time, this distant relative's life was in conflict. He held a lucrative position in his community's very powerful church, while at the same time he was publishing books on mathematics and astronomy, and believed that science was the key to communing with and understanding God -- an idea that ran counter to the powerful church doctrine of the age.
To protect himself, his position at the church, and his family, Zimmerman wrote his books under a false name. But was his secret life discovered by the church? Check out this exclusive clip to see what Groban learns about his ancestor.
This fascinating episode of Who Do You Think You Are? airs Sunday, March 15, at 10/9c on TLC.