'Bones' season 12 spoilers: Sully returns testing Brennan and Booth's already shaky relationship

"Bones" is unearthing a particularly old character and inserting him back into the lives of Bones (Emily Deschanel) and Booth (David Boreanaz). And while reunions are often fun, this might just come at a quite wrong time.

Tim Sullivan (Eddie McClintock) is making his surprising comeback into the series at some point in the upcoming last season of the crime/medical procedural. The old flame might be too old to rekindle but exec producer Michael Peterson hints that his presence can potentially still cause a rift between the married couple.

"He comes back at a time in Brennan's life when she is emotionally unbalanced," the show boss spilled to TVLine in a recent chit chat. "She and Booth are going through a very difficult time, so it's a strange time for this love from the past to show up. And it's going to have some slight reverberations. I'll be curious to see what the fans think."

Brennan's ex-beau traces all the way to the second season of the series when they got into a whirlwind romance that lasted for only a couple episodes. The romantic story progressed very quick but also ended in the same manner as well when the forensic anthropologist turned down Sully's proposition of an extended getaway. As it turns out, he wanted to embark on a life sailing into the Caribbean forcing Brennan to drop her life in the city. Obviously, this did not work out and the two separated ways. Since then, the returning character has been barely mentioned in the seasons to come which makes it all the more intriguing that he is being brought back at this particular time.

On top of dealing with a possibility of being sandwiched in a love triangle, Brennan appears to also need to keep her eyes open on other aspects of her life. An exclusive promo clip from Entertainment Weekly for the long-running drama teases of former Jeffersonian intern Zack (Eric Millegan) holding her captive. And despite her pleading eventually leading to mind games, the ex-apprentice appears to be motivated by his agenda.

"Bones" season 12 will consist of 12 episodes, the fewest chapter count in its history starting with the premiere coming on Jan. 3, 9 p.m. ET, on Fox.