Got a secret, and we don’t have to keep it!

Marlene King’s Pretty Little Liars spinoff pilot, Pretty Little Liars: The Perfectionists, is in the works – and star Sasha Pieterse is spilling major details!

“I think early next year we start filming, which will be very fun,’ Pieterse revealed to ET exclusively at Knott’s Scary Farm in Buena Park, California, on Friday night.

The 21-year-old starlet also told us that she’s had to keep the spinoff plans a secret for a year!

“I’m a good secret keeper, come on! On that show [PLL] for seven years? I know what to do. But yeah, seriously, it's really exciting. I love that it's new,” she said.

So what can we expect story-wise? And will any of the other ladies be making appearances?

“I'm sure that they will,” Pieterse teased. “We have to keep the PLL family alive, obviously -- and Emison, of course.”

*swoon*

But… Pieterse’s other half to Emison, Shay Mitchell, is set to star in a different Marlene King-produced series, The Heiresses. She says not to worry, though!

“I don't think that will be a problem at all. I think the fans will really appreciate it, so that's what we really care about anyway,” she explained after expressing her excitement for Mitchell’s new series.

”Marlene just really likes to keep it in the family, literally," Pieterse said. "She's such an amazing person. She's got such a big heart and we really love her so much, and the fact that we can all stick together somehow, really means a lot to us.”

As for where the spinoff picks up following the PLL finale? It seems not much time will have passed at all.

“I don't want to get in trouble, but I think it's a year or two [after],” Pieterse revealed.

“Honestly, I'm so glad that we're kind of picking up where we left off," she added. "We left it in such a good place and I'm excited to be a mom, hell yeah!”

So yes, expect those Emison babies to be running around!

“It’s just a fun, different experience and I'm glad that I get to continue the character," Pieterse noted. "She's amazing and I think, honestly, you'll see a little bit more of a feisty side of her now that she's in another element that she's not used to.”

In the meantime, Pieterse is gearing up for a sure-to-be stellar performance on Dancing With the Stars on Monday. She and partner Gleb Savchenko are dancing a Jazz number for “Guilty Pleasure” week. The song of choice? "I Can’t Help Myself (Sugar Pie, Honey Bunch)" by The Four Tops.

“My guilty pleasure is baking!” Pieterse exclaimed. Fitting, of course, seeing how she has an entire blog dedicated to her hobby.

“It’s a bake-off competition, so it's pretty much baking with the stars on a dance floor,” Savchenko chimed in.

“We compete always, anyway, so it comes natural,” added Pieterse of the pair’s theme.

For more from our interview with Pieterse, watch the video above. And for details on Mitchell’s other new series, You, watch the video below.

Will you be watching The Perfectionists? Let @Katie_Krause on Twitter!