Found this.
https://aeon.co/ideas/the-strange-story-of-inventing-the-bastard-in-medieval-europe
Excerpt
...‘bastard’ because of his mixed parentage: he bore both noble and ignoble blood, ‘obliquo sanguine’..
..Yet prior to the 13th century, legitimate marriage or its absence was not the key factor in determining quality of birth. Instead, what mattered was the social status of the parents – of the mother as well as of the father. Being born to the right parents, regardless of whether they were married according to the strictures of the Church, made a child seem more worthy of inheriting parents’ lands, properties and titles.
That is quite interesting. Seems to be how it works today.