Not sure how to feel about this.

[UmbrellasKeepFallingOnMyHead]

I have name changed to a little used old name as this is extremely identifying.
I'll try to be as factual as I can as I'm still numb and in shock and don't want to drip feed.
Last week I found out in an email from my Father that I may have a half brother. My Father seems pretty made up about it. He's actually known about the fact he may have another child for years so it's not really been a shock that this person has now come forward.
My parents split when I was a few years old and my Mother and I moved back to the UK. My Father and all my relatives on his side all live abroad. They never call and I just have an email relationship with them all. My Father wouldn't come to visit in the UK when I was a child as he was worried he'd be arrested for non child payments as he never paid my Mother a penny. It's like I was just a burden to him. Although the past few years we have slowly been building up a relationship .
I've seen photos of him and he's the spit of my Father. My Aunt is reserving judgement until the DNA test us back in five weeks. I
I'm just not sure how to feel.
My Mother has always been angry and bitter about my Father and now they have started emailing each other which I don't want to be dragged into as it's getting pretty poisonous.
My potential half brother has also been messaging me. I am replying with typical British politeness but inside I just want him to back off. I actually think like I'm about to fall apart and am pretty tearful, but I don't why it's affecting me so much.
I'm not sure what I'm asking really.

Maybe because your father seems excited about his son coming forward and you you feel your father hasn't really been bothered about you. It must feel very unfair.
An adjustment to being 'an only' child to having a (half) sibling.
You must be feeling a lot of different emotions xx
Bigs hugs

You don't have to have a relationship with him if you don't want to. I don't think I would in your situation.

My exH discovered his father had had another child a few years ago. He's never had anything to do with her and I doubt he ever will.

I'd totally step away.

Sounds like this has brought up all sorts of feelings of sadness and rejection at the way your father treated you. So protect yourself - you owe him and his potential son nothing, remember.

You can stop replying to the son.

And you can remind yourself that you don't owe your dad the favour of joining in and acknowledging his being 'made up' over his son. In fact, what your dad deserves is more like one big raised eyebrow - from you, his only other child, the only other person who KNOWS what a failure he is as a father. 'Made up'? Aye right, til he gets bored eh? Fuck off, 'dad'.

You don't have to play along. And don't feel slighted - sounds like he's just an immature idiot. Maybe comment that it must be his ideal scenario - a son to get excited about who is conveniently over the age where he might be required to pay maintenance, so he can act 'made up' without the fear that he might be asked to contribute something apart from empty words.

Your feelings and confusion is understandable. Remember that he didn't choose to have any involvement so you just do what is right for you.

As far as your mum is concerned, why is she still communicating with him? She shouldn't and she shouldn't bring you into it. Tell your mum that you understand why she's angry and that you're thankful that she raised you but that she really has to move on or leave you out of it.

My eldest's father has paid a penny nor been involved in his child Life for over a decade but I'm just grateful that I have my child and selfishly that I didn't have to share him. There's no point on dwelling on the bad points.

My Aunt is justified in stepping back. She thinks it's a scam. Apparently he has spent 20 years in prison. I emailed my Father and he is being vague about it, drink and drugs is all he said.
My Mother had apologized to me for trying to drag me in. I think it brought up memories of a bad time in her life so she lashed out. We have both decided to step away for now and wait for the DNA results. One good thing of not being on FB and in the UK will be that I won't have to see any of this. For now, I've muted them on WhatsApp and won't log into to the family email.

I would try to separate your brother from your father. He didn't choose to be born. Maybe wait until DNA results com back and go from there.