We already know that we'll be seeing more Frank (Tobias Menzies) in Season 3 of Outlander than book fans would expect, but it may not be the last we see of Claire's (Caitriona Balfe) first husband, or his evil 18th century ancestor.

Diana Gabaldon's book Voyager, on which the third season is based, is the last time Claire is in the 1900s. That means there aren't a lot of pages of Frank's story left in the book series. The show will already expand on Frank's presence by exploring what Claire's life was like with Frank after she returned through the rocks before the Battle of Culloden -- pregnant with Jamie's (Sam Heughan) child -- more deeply.

It's a period that Outlander executive producer Ron Moore says is necessary to understand who Claire is when she learns that Jamie survived Culloden 20 years after the fact.

Tobias Menzies, <em>Outlander</em>Tobias Menzies, Outlander

"The story requires [Frank]'s presence. Claire, from the beginning, was married to Frank and spent the entire first book trying to get back to him," Moore explained to TVGuide.com at the ATX Television Festival in Austin. "She's found the love of her life in Jamie Fraser, but there's still this man that has this hold on her so she feels like she needs to go back. That to me says that's a really strong character and an important character. To understand Claire, you need to understand the nature of that relationship with Frank."

Frank remains an important part of the story in Season 3 as we have to learn who Claire and their daughter Brianna (Sophie Skelton) have become in the time they spent with him in Boston.

"When she returns to the 20th century, Frank raises Brianna. Again, he's a very important figure in the story," Moore said. "He is the father figure that Brianna knew as opposed to Jamie. Claire spent 20 years with him before he died. We needed to bring that part of the story forward to really understand how all these things work."

Outlander Season 3: We Have to Wait a While to See Jamie and Claire Together Again

Voyager marks the last serious mentions of Frank and his 18th century counterpart Black Jack Randall in the Outlander book series. Frank dies in the 1960s and Black Jack is fated to die in the same battle Jamie survives. However, Season 3 may not be the last we see of Claire's first husband or the man who terrorized her and her husband in the past.

Moore admits that is in part because actor Tobias Menzies does such a tremendous job inhabiting both roles. The show isn't afraid to embrace future mentions of either character as a chance to bring Menzies back in later seasons.

"You never know. We've talked about it," Moore said about bringing Frank or Black Jack back. "There's always the possibility of flashing back and revisiting him in either role if we had a reason to. Diana in subsequent books kind of touches back to Frank for various reasons. We might do that. It really depends on how we break that in subsequent years."

That might sound like bad news to some fans who ardently love Claire with Jamie and would like to never be reminded of Frank -- but it's great news for anyone that loves seeing Menzies' incredible work on the show.

Outlander returns this September on Starz.