Dad tries to stop son from marrying stepsister.

This sounds like the premise of an adult film, but sometimes truth is stranger than (adult) fiction.

A dad going by the throwaway username throwawayQuestion667 claimed on Reddit's 'Am I The A**hole?' forum that his son is engaged to his stepdaughter, and he wants assurance that he's not a jerk for refusing to pay for the wedding.

He wrote:

When I married my wife, my son was 9 and my stepdaughter was 14. They grew up together and we all got along wonderfully.

My son is now 23 and both him and my stepdaughter have told us they're engaged. We had no idea they were even dating in any form.

I'm feeling very uncomfortable with this. I don't know when this relationship started, and I'm disgusted by the age difference implications.

My wife was shocked and isn't very happy either. But she's in the mindset that they're adults and aren't exactly blood related so we can't do anything about it, which I agree with.

But I've put my foot down on not contributing any money towards their wedding. And my son is aware that I'm not exactly thrilled with the relationship.

AITA?

This story made me barf. AITA?

It's straight out ofThe Brady Bunch Movie....or that infamous Folger's coffee commercial.

Things get worse, as the dad's ex-wife is now using the situation to hurt him even more.

'I'm actually being attacked nonstop by my ex who blames me for this situation. She blames me for bringing my stepdaughter around our son,' he wrote in a comment.

'And the sad part is I agree with her. I hate that I'm second guessing my marriage to the woman I love with all my heart.'

Plus, the son/stepbrother/fiancé won't tell his dad when the relationship started, which really ups the nauseating ante.

'My son isn't giving me an answer of when the relationship started and the five years [age] difference starts feeling very wrong depending on when their relationship started,' throwawayQuestion667 explained.

The internet is collectively nauseous.

Juror Kay_Sea425's opinion is that the dad is Not The A**hole (aka NTA).

'They're adults and can do what they want, but you absolutely don't have to pretend that you are a huge fan of this relationship or pay for the wedding,' they wrote. 'Also ick. What kind of reaction were they expecting?'

'NTA. i couldn't fathom ever dating or marrying any of my step siblings, past or present. it's just a line you don't cross,' dylanjpierce commented.

'NTA. Dude, they were raised as siblings since they were kids. That alone makes it nasty. The fact they won't tell you when they got together and it's a 5 year age gap makes it double nasty,' grumpyspudgal added.

Our thoughts and prayers are with this dad. Step-siblings are siblings, and society is rightfully disgusted by incest. There's a reason why Cersei and Jaime lied to Tywin his whole life.