'Riverdale': Did We Expose a Massive Cooper Family Secret? Lili Reinhart's Reaction is Priceless! (Exclusive)

Riverdale Cooper Family
The CW

WARNING: If you have not watched this week's episode of Riverdale, "Chapter 16: The Watcher in the Woods," leave now because we're about to discuss some serious Cooper family drama! For everyone else, get excited for some epic Riverdale secrets…

Hi, Polly! Bye, Polly!

This week's all-new episode of Riverdale finally treated fans to our first glimpse of Polly Cooper in season two, but this reunion with Berry's oh-so pregnant older sister was extremely short-lived when she decided to leave yet again.

It was revealed that the "Black Hood" killer has been targeting Riverdale's most sinful residents, and as an "unwed mother carrying her cousin's babies," Polly frantically decided that it would be best to take her unborn twins and get the hell out of town.

MORE: 'Riverdale' Star Cole Sprouse Reveals He and His Brother Dylan Were in a '5th Grade Gang' (Exclusive)

Riverdale Cooper Family
The CW

In this week's episode of Sweetwater Secrets -- your ultimate Riverdale after show on ET's YouTube channel -- series star Lili Reinhart admitted that Polly's déjà vu departure is going to be "devastating" for Betty.

"Betty feels a little cornered sometimes by her parents -- especially Alice, who's so aggressive and dominant," Reinhart explained. "I think Betty kind of felt like she had an ally with Polly there and that's why she tried so hard to find Polly in season one. So to have gone through all of that and then to have Polly leave so early after coming back, it's really devastating for Betty."

The blonde beauty continued, "But there's so many things that Betty's dealing with and there's so much on her plate that she can't stop and cry about it. She has to just keep moving on, but I think the biggest thing is that she lost an ally and someone on her side at home."

Luckily, the timeline in Riverdale seems to be moving pretty slowly. (By our TV expert calculations, all of the dark season one drama roughly took place over the course of just two months.) So it's not like Betty is going to miss the birth of Polly's twins… right?

WATCH: 'Riverdale' Star Lili Reinhart Reveals What It's Like to Film Those Intimate Scenes With Cole Sprouse

Reinhart simply answered us with a coy knowing smile. "You touched on something," she teased. When we pressed Reinhart to elaborate more, the actress quickly clammed up, which seems to further confirm the theory that Polly's pregnancy is going to end much sooner than expected.

Dun dun duuuun!

What you think, Riverbabes? Do you think we stumbled on a massive Cooper family spoiler? Tweet @LeanneAguilera with your thoughts and catch even more exclusive interviews with the Riverdale cast in this week's episode of Sweetwater Secrets on YouTube!

Riverdale airs Wednesdays at 8 p.m. ET/PT on The CW.