Raymond Coffer has put up a very interesting website, based on his doctoral thesis about Austrian expressionist Richard Gerstl. Gerstl is interesting for his work, as well as the fact of his brief and disastrous liaison with Arnold Schoenberg's wife, Mathilde. 

Coffer's website, in addition to covering the biographical and historical background of Gerstl and his notable contemporaries, also strives to illustrate the impact of this Schoenberg love triangle on Gerstl's work and the work of Schoenberg and his contemporaries (especially the direct effects of Mathilde's infidelity on Schoenberg's output during that time). I highly recommend diving into the fascinating research this site offers! 

In Coffer's words: 

"This website therefore reflects a welter of new documentary, oral, forensic, circumstantial and other evidence uncovered during my doctoral research, much of which relates to the extent to which Gerstl, Schönberg and others represented the sequence of events surrounding the affair in their creative output."

The painting in the header is a group portrait with Schoenberg and Zemlinsky!

Citation from Coffer's website:

RG65 Gruppenbildnis mit Schönberg, Gmunden, late July 1908
Oil on canvas, 169 x 110 cms. Signed: “Richard Gerstl”, inscribed verso:“Richard Gerstl, IX, Nußdorferstr. 35”. Stiftung Sammlung Kamm – Kunsthaus Zug.
Schönberg stands top left, Zemlinsky seated below him next to Ida and Mathilde. The third couple are not identified, but may be Karl Horwitz (Schönberg’s student) and his wife, Mizzi, who were on honeymoon. A sunstrewn backdrop, applied with a palette knife, shares the rich ochres and greens that typified Gerstl’s Gmunden portraits from 1908. Here, though, Gerstl stretched his evolving techniques, distorting faces, so that indistinguishable close up, they become gradually recognisable as the viewer draws back.
Kallir 49 – exhibited at Neue Galerie from opening, 28 September 1931.