Here’s what the internet had to say.
“I’ll forgive you for going to the ceremony but not the reception. I feel there’s a 90% chance grandma wanted you there for the bride to see that you were pregnant if everyone knew that she didn’t know.”
“Otherwise Grandma might have genuinely thought that you were attending the wedding as part of the family.”
“Your ex is horrid though. Who gets married without talking about kids?”
“I have a sneaking suspicion that grandma planned for all this to happen. Clearly the (briefly) wife didn’t know about the baby and she definitely deserved to know. I’m wondering if grandma coaxed (you) into attending specifically to let the bride know.”
“I’d cause a scene too if I not only invested money, but time, love and effort into something and someone that wasn’t even invited to said thing caused the whole thing to burn down in front of my eyes.”
“You were right to let the bride know that her partner was going to have a child with someone other than her, but you really should have done it before the wedding and let her choose how to deal with her partner rather than doing it so publicly.”