'Bones' season 12 episode 8 spoilers: Old flame poses threat to Brennan and Booth's marriage?

Eddie McClintock reprises role as FBI Special Agent Tim "Sully" Sullivan in the next episode of "Bones: The Final Chapter." | YouTube/FOX

Grief over Max's (Ryan O'Neal) death creates a rift between Brennan (Emily Deschanel) and her husband, Booth (David Boreanaz), in the next episode of "Bones: The Final Chapter."

Every person has his or her own personal ways of handling grief, which, more often than not, can pull even the most closely bonded couple apart. And the way Brennan deals with her father's death will greatly differ with how Booth chooses to face it. Thus, a gap in their relationship inevitably forms. Will this get in the way of their home and work lives? Will they be able to work things out soon enough to comfort their children?

To further complicate things, a significant person from Brennan's past shows up in the episode aptly titled "The Grief and the Girl." Long-time viewers of FOX's crime drama series may remember Brennan's previous love interest, Sully (Eddie McClintock), from the show's sophomore season. He's the guy who named his boat after Brennan, only to have his invitation to take a cruise on it rejected. After appearing in a four-episode arc, he was never heard from again until now.

The trailer for the next episode provides more clues on what's about to unfold when "the only guy, besides Booth, who ever stood a chance" shows up on Brennan's period of mourning. What could be the reason for Sully's visit? Is it to simply comfort a friend or to seek assistance with a case? Either way, the fact that Sully seems to be the only one who can reach out to Brennan when her own husband hardly could, may spell trouble for Booth and Brennan's relationship.

Will this really be the beginning of the end for the show's main couple, or will Brennan eventually let Booth in to share in her grief and bridge the gap between them before it becomes irreparable? Will Sully help bring the couple to this possible conclusion, or will he take advantage of the situation for his own gain?

The next episode of "Bones: The Final Chapter" airs on Tuesday, Feb. 21, at 9:01 p.m. on FOX.