AITA for son disrespecting my last name.

My son 26, is getting married to his fiancé also 26. They have been together since high school and she is a wonderful person who we really love. But when they get married instead of her taking his name or hyphenating their names they are going to combine their names.
This all started when she wanted to keep her last name because she is the last one with her last name in her family. No problem, we thought hyphenate or keep her name. Nope. They have decided to combine their names which totally defeats her original purpose of keeping her last name.
My family including myself feels that my son is being disrespectful to my family name by doing this.
I know he will always be my son and always my last name in my heart, but feel offended and hurt that he is going to make up a last name. My ex thinks it’s cute what they are doing?
Am I overreacting and being an a-hole over the family name?