What happened to Mila Munch's children's father?

Thinking on Gunther the past few hours, he can't be Jacques because Gunther doesn't have beady eyes and a prominent brow line. Going back to genetics, it's almost certain that if Gunther was Jacques child, he'd have a stronger resembalance to to his father, he also have a fatter looking face because of Mila's features and a more prononced brow line and chin from Jacques, however the hair colour fits together, so there is that.