I know people have the right to invite who they want to their party and I totally accept that but this boy is one of DS1's good friends so I am surprised that he wasn't invited.
The party was a couple of weeks ago but have only just found out as one of the other mums asked me why DS1 didn't go knowing that they were good friends.
This boy's mum was one of the first mums I got chatting to when they started school a couple of years ago and initially we organised playdates etc but it has tailed off - on my part, due to time as I work 4 days a week etc but no idea why it tailed off on the other mum's part. We don't really see each other at the school gate either as I only do drop-off twice a week and she is always late so not there to chat to and both boys go to after-school club 3 or 4 times a week so don't see her at pick-up time either.
DH thinks it is because I had the audacity to speak occasionally to her next-door neighbours who she hates with a vengeance 
Again. I don't have a problem with it but I think it is unfair on DS1 to not be invited to one of his friend's party because the mum has some kind of problem with me - however, 2 days before the party, we went to a literacy evening at school and she couldn't have been more friendly with me
Had she snubbed me at that evening it would make more sense that DS1 wasn't invited.
Dh thinks I should ask her next time I see her if X had a nice birthday party and watch her squirm see what she says.