The Bold and the Beautiful spoilers: Luna's paternity shatters Steffy and Finn's relationship?

If Luna is revealed to be Finn’s half sister on The Bold and the Beautiful, it has the potential to shatter Finn and Steffy’s relationship.

Poor Finn (Tanner Novan) can’t catch a break. It’s bad enough that his birth mother is the notorious killer Sheila Carter (Kimberlin Brown). But if it turns out that Luna (Lisa Yamada) is his half-sister through his father Jack’s (Ted King) affair with his aunt Poppy (Romy Park), then things could get even worse.

We talked about all the reasons why Luna’s paternity matters to several characters on the show. She has ties to lots of people, and it doesn’t help that she’s living with Bill (Don Diamont).

But when it comes to Finn, Luna’s paternity could destroy his relationship with Steffy (Jacqueline MacInnes Wood) after all the work they’ve done to get back to a very strong and secure place in their marriage.

Finn spent most of last year and a significant chunk of the year before that trying to figure out his connection to his birth mother. He persisted in the endeavor even though it hurt Steffy. While we understand Finn’s confusion on the issue, we also fully understand why Steffy didn’t want her husband around Sheila — after all, Sheila tried to kill them both.

That right there is why Luna’s paternity is such a massive threat to Finn and Steffy’s relationship. If Luna ends up being Finn’s half-sister through his father, we think he’ll want to try to figure out how she fits into his life. She won’t just be his cousin anymore, she’ll be his half-sister. And Finn, ever the Boy Scout, will want to be there to help her through her struggles as Jack presumably tries to get her out of jail.

All of this sounds noble until you recall that Luna almost killed Steffy. After Steffy put the pieces together, Luna drugged Steffy and locked her in a cage, leaving her to die when her old apartment building was demolished.

We know all too well that Steffy did not support Finn’s desire to have a relationship with Sheila (which is why he cut ties with her), so it’s not hard to imagine Steffy issuing the same demand to Finn. Unlike Sheila, though, Finn will see his cousin (now half-sister) needing his help and he’ll feel compelled to support her because they’re family and he watched her grow up. They have history together. And we don’t think Finn will be able to turn his back.

This won’t go over well with Steffy. First Sheila, and now Luna? (Let’s also take a moment to reflect on the fact that poor Finn has two murderers in his family!) We don’t blame Steffy a bit for not wanting her husband to have a relationship with the person who tried to kill her, but it’s hard to imagine that Finn won’t at least try to be there for his new half-sister in some capacity.

Needless to say, this could be the straw that breaks the ol’ camel’s back when it comes to SINN. For now, all we can do is wait and see what happens.

The Bold and the Beautiful airs weekdays on CBS and the following day on Paramount Plus. Check your local listings to see when it comes on where you are.