Is it proper to invite my father's ex-wife to his and my mother's wedding anniversay party?

My step-siblings and I are having a surprise wedding anniversary party for our parents. They added their mom to the guest list. I believe it would be improper and awkward for her to be at her ex's anniversary party. And I'm sure my mom would feel awkward too. They have a "cordial relationship." They aren't "best friends" and hardly see or communicate with each other. I think since the celebration has nothing to do with her kids, it's for her ex-husband and his present wife she shouldn't be invited.

Jun 03, 2011
Anniversary Party
by: Wendy (Modern Manners and Etiquette)

Thank you for your question.
I agree with your feelings about inviting your Father's ex-wife to an anniversary party. It is a great thing to throw a surprise party for them, however I do not think that the surprise of his ex-wife would be one that he would enjoy.

The anniversary party is to celebrate the relationship of your Father and his new wife. If you were throwing a surprise birthday party for one of his children with his ex-wife, then definitely she should be invited.

As neither one would be comfortable with her attending the party, it is best that she not be included.