Telling a fairly new friend that her ex-husband is bad-mouthing her at school

[Scootergrrrl]

Would you tell a fairly new friend that her ex is really rubbishing her at the school gate when he's picking up their children?
As I was waiting to go into school this afternoon, a man I'd never seen before was holding forth about the unfairness of the access system, CAFCAS being rubbish and his ex-wife being a cow and trying to poison his children against him. It's a small school and I worked out quite quickly he was talking about a new friend of mine - they've recently moved to the area. He didn't mention her by name but did name the children so it would be easy for anyone to work out who he was talking about.
Should I tell her what he's saying? I'm aware there's two sides to every story etc etc but he really did sound quite nasty. Or is it none of my business?

I'd tell her as she might need to talk to the school about his behaviour

He was there to collect the children for a pre-arranged access visit so my friend knew he was there - not just randomly hanging around being foul about her. Does that make any difference?

Is this just the once you've encountered him?

If so, I'd be tempted to hold off for a while. You don't know if this is a one-off out-of-character outburst. i'd keep an eye on it, though as I'd rethink if I noticed a regular pattern.

Its the first time he's been up since they arrived a couple of months ago. He did strike me as a bit of a nasty piece of work.

If he strikes as a nasty piece of work then I am sure others whom come across him will probably think the same.

I really don't know if you should or shouldn't... Ummmm.... Perhaps see if he continues to be a gobshite? If so then say?

He was being really quite vile. And smoking just outside the school gate which I didn't like either (entirely irrelevant, I know but there you go). Any more advice for me before I see her tomorrow?

Could you say to him you'd rather not hear his negative comments?