Co parenting conundrum involving new partner!!!!

[whatdoyouthink12345]

I've name changed for this, so I won't be returning after this OP but would love to know the general opinion on this one and I'll be reading the replies (if I get any!!).
This situation is NOT about me for starters so that's why I'm talking in the TP 🙈.

Parents split up over 5 years ago. No reconciliation and both moved on with their lives.
Thjngs are mainly amicable, but dad is a liar and manipulator so mum is always treading on egg shells and worries when they are away.
Two children, one with SEN. Both under 8.
Mainly live with Mum but see dad on set day/night.
Dad has a new partner. I say new, they've been together a couple years. Only met children recently though. Mum asked to meet new GF when she started to spend time with children, dad said no.
Mum is a very gentle person, she is not argumentative or confrontational in the slightest.

So that's the back story.

Eldest DS has told mum today that his dads gf has moved in with them. Mum was shocked and had thought dad should've mentioned it to her. Not for her permission or opinion, but as a general respectful thing to do. A parent should know who their child is living with right or any significant changes in their home?
So what do you guys think...

Is it reasonable for Mum to have expected dad to tell her GF was moving in with him and the kids?
Or is it reasonable for mum to find out via child?

Mum won't be bringing it up regardless because there's no point and would get more of a response out of a brick wall!

He definitely should have said. She should raise this with him- brick wall or not!

As dad is a liar, a manipulator and knows that his ex wife is too gentle to bring anything up, it is naive to expect him to offer info like his partner moving in.

Things are probably mainly amicable because she’s scared to bring things up. Manipulators are inevitably going to be happiest when they are getting their own way.

He should have told her.

What’s right and what’s reasonable are neither here or there as he’s a manipulative liar around whom everyone has to tread on eggshells.

You would be VV unreasonable to expect him to behave considerately at this stage. He couldn’t be considerate while he was with you, why would he start now?

How is communication between exH and your friend otherwise? Yes, it would have been courteous but isn't an actual requirement.

Yes he should have told her as a matter of courtesy but sounds like he’s one of those where she needs to pick her battles, and this isn’t one of them.