Kate's Past on 'This Is Us' Is Still Shrouded in Mystery, but Things Won't End Well

Kate is going through some major life obstacles as an adult on This Is Us, but teenage Kate is just as lost right now. As soon as her boyfriend, Marc, came into the picture, fans were skeptical of him and what sort of impact he might have had on her teen years. Kate and Rebecca alluded to it as much when they cryptically talked about not seeing what would happen with him at the time and having regrets about it.

Then, in Randall’s episode of the latest Big Three arc, a teenage Kevin tells Randall there’s an emergency with Kate. Another flashback showed Kate talking to her boyfriend on the phone and asking him if she did something wrong. On the surface, it certainly seems like there is an upcoming reveal that paints even more tragedy in Kate’s past. For now, though, it could be anything.

The questions and theories about what happened to Kate began when she and Rebecca uncovered some old Polaroids in the family piano bench in present day. While looking at the photos, Rebecca told Kate, "I was trying so hard to hold it together that year after your father died. And I wanted to believe so badly that you kids were happy, I didn’t see what was happening." Kate replied that she "didn’t see it either," which led some fans to believe the worst about Kate’s boyfriend from her teen years.

Almost immediately, fans began theorizing about all of the ways things might have went wrong in Kate and Marc’s relationship. The most popular idea among fans is that Kate’s boyfriend turned out to be controlling and no one saw it was happening before Kate felt too attached to him to do anything about it. This could also play into Kate’s ongoing issues with overeating, which started shortly after Jack died.

One theory about what happened to Kate on This Is Us says that Marc actually died and Kate blames herself for the death. According to the theory, when Kate was shown talking to Marc on the phone in a flashback, they were arguing. Then, he picked her up and they were in an accident, resulting in his coma and a minor injury for Kate. Thus, the reason Randall had to head home for a family emergency in his Big Three episode.

Regardless of what happened to Kate in her teen years, This Is Us executive producer Isaac Aptaker revealed to Entertainment Weekly that fans should be worried about Kate as she gets deeper into her relationship with Marc. It’s unclear how serious things will get, but the relationship probably won't end well.

"Fans should have a healthy amount of concern. I mean, there’s something ominous looming there, the way that Rebecca and Kate are speaking about that relationship in present day." Isaac said. "And although he seems like a sweet guy now, it certainly seems like that did not end well for Kate."

As Kate’s Big Three episode draws closer, the reality of what happened to her will likely be revealed. Until then, it’s hard not to consider the worst.

Watch This Is Us on Tuesdays at 9 p.m. ET on NBC.