'Unexpected': 15-Year-Old Graham Struggling After Girlfriend Kayleigh's Pregnancy Reveal in Exclusive Sneak Peek

Unexpected star Graham is struggling with the news that he'll soon become a teenage father after his girlfriend Kayleigh learned she was pregnant. In a PopCulture.com exclusive sneak peek of Monday's all-new episode of the TLC show , the mother of 15-year-old father-to-be Graham speaks candidly about the pregnancy that turned everyone's world upside down and the impact it has had on her son's health.

At 42 years old, Bekki is about to become a grandmother to Graham's child with 15-year-old girlfriend Kayleigh - news that came as a total shock to both her and Kayleigh's mom Mandy. "The day I found out that Kayleigh was pregnant and Graham was gonna be a father, I went to sleep [and] when I woke up, I looked on my phone [and] I had several text messages, several missed calls ... from Mandy," she remembers. "So I called her and she's like, 'Kayleigh is, you know, pregnant.' And I'm like, 'Huh?' I could not process it in my mind. I didn't know what to do."

She continues, "Mandy was bawling and I remember repeating myself saying, 'I'm sorry, I'm sorry, I'm sorry.' I just felt like it was my fault that all this happened because I believed that they were having sex in my house ." Bekki admits that after leaving Graham home alone some days, she would return to find Kayleigh there with him. "So they could have been alone for an hour. They could have been alone for two hours," she confesses. "And in an hour and two hours, there's a lot of things you can do during that time."

The news of Kayleigh's pregnancy has hit Graham hard, and Bekki says he hasn't been "eating a lot" since getting the news. Kayleigh explains, "After Graham figured out that he was gonna be a dad, I could tell he was stressed out a lot, but I didn't think it [would] impact like his weight and everything and like his health. But he's thrown up a lot, a lot."

In footage of a FaceTime between the two teen parents, Graham can be seen telling Kayleigh, "I got bubble guts. I threw up in the sink," as she responds, "Bro, what the crap?" Graham tells the camera, "I lost 15 pounds in like a month almost, and then just been going down from there." Lightening the mood, Kayleigh teases, "Teach me your diet," before insisting, "I'm joking. I'm joking."

Unexpected airs Mondays at 9 p.m. ET on TLC.