come to find out

[yuriya]

I lived most of a life thinking thinking things were one way. Come to find out it wasn't that way at all. I can't say I'm happy about it, but I guess I don't have a choice, do I?

I wonder why come is used instead of came in the above sentence. Is it short for I've come to find out? Come to think of it, come in the phrase come to think of it is used this way? That is, short for now that I've come to think of it?

[corum]

IMO the story goes like this:
The subject of the sentence and the helping verb 'have' have been dropped. It is a common practice in informal register.

(I have) come to find out...