How should I respond?

I never knew my dad, but apparently he had a son a little older than me, and he messages me out of the blue saying he’s my half brother and that I have a nephew, etc. My mom said he really was. How should I respond to him? He just said Hi, you don’t know me, but I’m your half brother, and you have a nephew. That’s all he said
Answers

Gypsyfish

Say hello, and that you're excited to find out about him and your nephew. Ask where they live. Tell him a little about you. Exchange a few messages, then see if there's any way you can meet in person.

Alex

Don't panic, and punch him in the face I'm just kidding, just act nicely and say Hi i guess I am ur half sister/brother. Guessing you would have a tough time

Pearl L

ask if you can nneet hinn sonnetinne

Marie And Alan

Why not meet up if you live near enough? Such relationships can be very rewarding.

real estate guy

If you are mad, the problem is with your father. This guy didn't do anything to you so you should have NO ill feelings against him. He basically is in the same boat as you. What do you want to do. You can do nothing and forget it. You can reply or call him and talk. It's up to you.