That phrase is a cliffhanger, but there’s no way to tell “who it is” without the full context.
“Who it is—it will break your heart” is usually used in:
- celebrity gossip teasers
- relationship rumor posts
- or emotional story clickbait
It’s designed to make you curious without giving real information.
If you paste the full sentence or the paragraph it came from, I can tell you exactly what it’s referring to and whether it’s real or just a misleading hook.