Grudd Anders Zorn was one of the best watercolor painters ever and had an interesting background, not least when you look at some of the details. The brewer Leonard Zorn immigrated from Germany January 14th 1860, which is too late for him to father the illegitimate child, born February 18th 1860 as the son of farm maiden and bottle rinser Grudd Anna Andersdotter. That might be why Anders and Leonard didn’t share any facial traits and why Leonard’s collegue Franz Heiss, who came to Sweden the year before, seems to have passed on the shape of his eyelids, forehead and ears to the artist. He also cared for him a lot and called him his dear friend. Maybe he had a reason to call him his dear son?
The Port of Hamburg, Anders Zorn 1891
Anders Zorn and his wife Emma in 1880
Franz Heiss (detail) by Anders Zorn 1902
Update August 26th 2015
Anders Zorn obviously painted this portrait a couple of years after Frans Heiss' death. He might have used a photo reference - he often did - or depicted the brewer's son by the same name.