The episode itself ends on a cliffhanger and does not officially reveal who the third heart smashed is yet, so there is no 100% confirmed answer in the show at this point.

However, fans have done a lot of frame‑by‑frame sleuthing and behind‑the‑scenes matching, and the overwhelming theory is that the third smashed heart belongs to Catey.

Articles and forum breakdowns point out that:

  • The design of the heart Nick smashes at the end matches Catey’s heart (specific streaky inner outline).
  • Camera angles and podium positions line up with where Catey stood in the game.
  • Behind‑the‑scenes and trailer shots suggest she’s missing while others clearly appear in later scenes.

So: on-screen it’s still a mystery, but the best-supported community consensus right now is that the third heart smashed is Catey’s.