Recognized the thread title from the previous thread. Wow, that escalated FAST.
OP, I'm sorry that these immature cowards have chosen the occasion of their wedding - supposedly two people celebrating their love - to send you this hostile, passive-aggressive message that they have no value or regard for you whatsoever. And there's no mistaking this was their intent. Quoting your update:
Yes, it seems my EX husband and his DP (The Gin Queen) have been invited to the wedding. How privileged are they?
I'm afraid this, on top of the rude 'expectation' that you'll deliver your mother to the event and then sit outside like a spare part, seems to clinch it. This isn't accidental, or even a decision taken in view of numbers, expenses etc. It's a calculated insult, it was intended to wound, and it was probably done in retaliation for some perceived or unintentional slight that you were unaware had even happened.
This, unfortunately, is how passive-aggressives operate. It's just craven cowardice: most normal people with the ability to communicate as adults would have nipped this in the bud with a frank conversation before it ever got this far. Unfortunately, I've taken a decade-and-a-half of the same sort of behaviour from my in-laws, so I speak from experience.
It's never nice when the scales fall from your eyes and you see the truth of what person really is - it's bloody painful, in fact - but I think your mother was very wise in her comments. I'd be inclined to draw a line under this one now and not give this idiotic Groomzilla any more of the drama he clearly craves. In a way, both he and his fiancee are worthy of pity. Whatever this wedding is about, it's certainly not 'love'.