How would you feel of your partner told you they were trans after youve dated for a long time?

I saw some questions regarding this on the trans sub - and a lot of people gave advice 'don't tell them you're trans, just say you can't have kids'.

Don't get me wrong, I'm not transphobic but I feel like it's a massive thing to hide from a partner, and it's very deceiving to keep that from them.

If the scenario was:

You were dating a woman (a post up trans woman) so physically looked like a woman. Maybe for 10+ months or even a few years. Maybe even married them. You've been sexual with them.

Then you found out that they were born a male, and have fully transitioned. How would you feel in that situation? Would you stay in the relationship?