The use of the word 'rear' may imply that he is not his biological father but only an adoptive one? 'Sire' could've been used to make it clearer. Mavis is clearly named as his mom so I'm not entirely sure.
As expected Kagura stood no chance against Larcade.But for Mavis being his mother Zeref might took a sample of her DNA after she fell into coma and gave birth to him artificially.