Noah Wyle is digging into his roots.

On Sunday's episode of Who Do You Think You Are?, the ER star gets some answers about his mother's family line and discovers the truth about an ancestor's role in one of the bloodiest battles in the Civil War.

In ET's exclusive sneak peek, Wyle learns that his ancestor John Henry -- who he believed to have paid someone else to take his place on the battlefield -- actually did fight in the Battle of Shiloh in April 1862, nearly a month after enlisting.

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Wyle asked why Henry, who was born in New York, would fight for the South in the Civil War and finds out that he had been living in the region for a time, likely with some ties to slavery -- though it's unclear for what length of time.

"I'm fascinated by this because this is kind of cool to find out that he had enlisted and served in the Battle of Shiloh, diametrically opposed to the impression I had been given, that he had paid someone to fight for him," the 45-year-old actor said. Watch the video above for more.

Who Do You Think You Are? airs Sundays at 10 p.m. ET/PT on TLC.

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