Sunday night's "Shameless" shocker -- Karen's (Laura Wiggins) pregnancy -- may have serious consequences for the Gallagher family, especially for older siblings Fiona (Emmy Rossum) and Lip (Jeremy Allen White), who will face off in an explosive argument before the season's end.

"It's incredibly frustrating for Lip because he's done so much for the family, and the first time that he asks for any help in return, the family comes up somewhat empty-handed," White told HuffPost TV in December. "I think that there's a great sense of betrayal that Lip feels halfway through the season."

Lip has to contend not just with the weight of his impending fatherhood but also with the wrath of his older sister Fiona, who is not happy about Karen's pregnancy.

"Fiona doesn't like Karen," Rossum recently told HuffPost TV. "She thinks that Karen is the town bike, which she is, and Fiona doesn't trust her. She thinks that Karen is manipulative, so Fiona doesn't have a lot of love for Karen. She supports Lip in what he wants, but she's really mad about this possibility of Karen having a baby and it maybe being Lip's."

In the wake of the unplanned news, Lip makes a few questionable decisions -- and that's where things between Fiona and Lip start to unravel.

"Fiona is sacrificing so much so that Lip can have a better life, and he doesn't want it for himself," said Rossum. "That really makes Fiona angry."

The blow-up between the two Gallagher siblings will even cause Lip to leave the house in a very Frank-like manner.

"It's a pretty big moment for the family," revealed Rossum. "Fiona and Lip are arguing about how he's living his life and how he deals with Karen's pregnancy because how he deals with that and how Fiona wants him to deal with that are very different. They don't see eye-to-eye, so they have this big fight, and Fiona basically gives him an ultimatum that causes Lip to leave."

After leaving the Gallagher house -- his undoubted safety net -- Lip, like his deadbeat alcoholic father, spends the day going from house to house, looking for a place to crash. It looks like the apple doesn't fall far from the tree in this dysfunctional family.

Amid all the drama, however, there is something to look forward to for fans of Fiona and Steve (Justin Chatwin). After Fiona's desperate phone call in Sunday night's episode, Steve's return to Chicago may come sooner than expected.

"Fiona accepts an invitation to go to a wedding with this guy she's been seeing, and after this wedding goes horribly wrong, she comes back at another low point, feeling awful," Rossum said. "And he just so happens to be standing on a street corner. She's not expecting him to come back."

But just because Steve is back in Fiona's life, don't expect them to get together ... yet.

"He reveals some things about his life that make it almost impossible for them to be together initially," explained Rossum. "We're going to see them wanting to be together, but they need to face this obstacle first."

"Shameless" airs Sunday nights at 9 p.m. EST on Showtime.

Related on HuffPost: