Who do te think could've been Master Makarov's wife? o at least what do te think happened to her? Is Ivan an adopted son?

Laxus look almost 100% identical to the young Makarov so there is no doubt that Laxus is his grandson which means that Ivan is Makarov' biological son.Its still strange that Makarov's wife was never mentioned.My only guess would be that Ivan is an illegitimate child.His mother probably died o left them.Since they didn't get married,she doesn't count as being his wife.