Warning: This post contains spoilers fromFirefly Laneseason 2, part 1.

Kate (Sarah Chalke) and Tully (Katherine Heigl) have been through a lot.

So what could possibly have torn them apart?

Sarah Chalke and Katherine Heigl on ‘Firefly Lane’

Sarah Chalke and Katherine Heigl on ‘Firefly Lane’.Diyah Pera/Netflix

Kate had just found out that she has cancer, and Tully wasn’t home.

SARAH CHALKE:No.

You go back and forth?!

Firefly Lane. Sarah Chalke as Kate in episode 209 of Firefly Lane

Sarah Chalke on ‘Firefly Lane’.Diyah Pera/Netflix

[Laughs]But the clothes help.

Everybody knows each other and you just fall back into it so quickly.

We knew it was something big and unforgivable and I was so curious what it was gonna be.

Because I felt like, “What could break up this unbreakable friendship?”

And what I loved about it was that you really see both sides.

I think the context of everything she went through in season 1, it makes you really believe that.

I felt the same way when I read it.

I was like, “Okay, good for Kate.”

And I also love that scene because nothing is straightforward.

You understand where Tully’s coming from, but Kate can’t because it was Marah.

Maybe if it was Kate it would be different, but it was Marah, it was her baby.

I imagine you knew the cancer twist was coming, right?

Well that image of her outside Tully’s door alone is so sad!

It’s the saddest image!

I’m excited for everyone to see it.

But there’s also lots of levity.

This story was intimidating.

I didn’t know what that was going feel like to play her journey.

So there was definitely some emotional days on the set.

This interview has been edited and condensed for length and clarity.

Firefly Laneseason 2, part 1 is out on Netflix now.