https://allthatsinteresting.com/alois-hitler

Alois Hitler wanted to marry his cousin immediately, however, their close relation posed some legal difficulties and they had to request a dispensation from the local bishop. The bishop was clearly also disturbed by the very few degrees of separation between the pair and forwarded the request to the Vatican, who eventually granted it (perhaps because by this time Klara was already pregnant).

https://www.quora.com/Why-did-Clara-Hitler-marry-her-cousin