My friend is getting married and his ex/mother of his child is REFUSING to let their 8 year old be a part of the wedding or even attend. I think she's petty and mean. Would you let your child be in or at least attend their other parent's wedding?

My friend never got married to his ex. They busted up when the kid was 3. They've always had a decent co-parenting relationship and there seemed to be no bad blood. She didn't seem pissed or bitter when he started dating. She even said congratulations when they announced their engagement. This is totally out of the blue. They split time basically 50/50. They've rearranged weekends and holidays when one had something come up many times before, so I really don't think this is because it's on "her time". He has no idea what to do. The kid is upset that they can't be with daddy on his wedding day but the mom won't budge. Thoughts?