'Bones' season 12 spoilers: Brennan's ex-boyfriend returns; EP hints 'strange' finale storyline

"Bones" returns with all-new episodes next week, and it seems that the farewell season will be seeing some tension between Booth (David Boreanaz) and Brennan (Emily Deschanel).

With the Fox crime series heading into its final season, some familiar faces are expected to return, including Eddie McClintock as Brennan's ex-boyfriend, Tim "Sully" Sullivan. His arrival will happen during a tense period for the mystery-solving duo, and Sully may take advantage of Brennan's vulnerable state.

In a recent interview with TV Line, executive producer Michael Peterson teased that Sully's comeback will cause a complication that affects Brennan and Booth's relationship. "He comes back at a time in Brennan's life when she is emotionally unbalanced," Peterson said. "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," he added.

Sully made his last appearance in season 2 when he was still dating Brennan. The agent wanted to live his life to the fullest after he lost his FBI partner, so he asked Brennan to sail with him to the Caribbean in a boat he named after her. Unfortunately, she declined his offer, and they decided to part ways after that. Since his exit, his name was not mentioned by any character on the show.

On another note, the series will reportedly end with a two-part special episode titled "The End In The End." While wrapping up the storyline, the said episode will also show the major characters in a different light. As Peterson puts it, the finale is going to be something fans wouldn't expect. "It's going to cover a 24-hour period of time, and it gives a lot of setup for Episode 12," he hinted, adding, "It's a very strange episode."

The 12th and final season of "Bones" premieres on Tuesday, Jan. 3, at 9 p.m. ET on Fox.