DD introduced to unknown adult half sibling by exp

[Arrgghhhhh]

Some advice please. Ex P (seperated 8 months ago) has an 18 year old adult child by a previous partner & 2 children (10&8) by another ex partner. Before & while we were together he had no contact or interest in them (I know red flags in hindsight)
He's not currently in a good co parenting routine with me because he essentially doesn't want to parent & just wants to babysit a few hours here & there with occasional overnights, though his parents are helping encourage & establish a better way forward. He prefers to drink & socialise on his days off & doesn't want to or see the benefits of a routine for our DD.
Roll on yesterday and my DD says when she was with exp he collected her big half brother & went to Nanny's for dinner ! She didn't know she had any half siblings until that moment.
I'm not sure how I feel or how to go forward - I'm not comfortable with another adult male unknown to me being in her company where she may be unsupervised ie at his house. ExP doesn't know his son hasn't met him more than 2/3 times in his life. I'm worried he's 'matey' with him & will have him over drinking with my DD there overnight.
He doesn't find the time to parent his littlest child but now his eldest is 18 is now present in his life.
Sorry for rambling - finding it hard to not know who's around DD all the time when not with my family or at school.
Found this all out from DD as he hasn't even had the manners to mention it.

Sadly in his time it's his decision.
I had concerns about ex drinking at a mate's house and dc sleeping on a chair until he took them home. Walking back in the dark - both under 5.. Different parenting styles in was told
..
No fucking parenting imo.
At best teach your dc to stay safe around all adults.
Try not to quiz them too much. Ime it can result in guilt for enjoying time with the nrp...
Yanbu to expect better but surely you know he is a prize twat already? Hence the ex.

Not really much you can do ...he has PR and its up to him who your DD spends time with ..... unless your DD says he has been abusive

Yes unfortunately there is nothing you can do to stop him having his older son there with him.
If you're worried about abuse then even if your ex knew his son he wouldn't actually know he was an abuser because it's generally hidden from everyone. I'm not saying that to frighten you, but 'knowing' him means nothing.

As for the drinking then I don't think you can stop that either unless your child was clearly in danger.