Like many posterists, Grün started painting as a hobby-mostly still lifes and portraits. He studied under Antoine Guillemet, the renowned landscape painter and longtime Jury member of the Salon des Artistes Francais. Grun revered his relationship with Guillemet. He paid hommage to his mentor by painting him in many of his paintings, including Fin de Souper (The Dinner Party) and un Vendredi au Salon Artistes Francais.

Image: Antoine Guillemet, from Grun's 1911 un Vendredi au Salon Artistes Francais

Image: Antoine Guillemet, from Grun's 1913 Fin de Souper. In this particular piece, he is shown chatting with Grun's wife, Juliette Toutain-Grun, after dinner.

In the excerpt below, taken from a French periodical toward the end of his career, Grun recalls his experiences and tutelage under Guillemet (translated from the original French):

One day (it was in 1887 and I had already a workshop), one of my friends came to see me. He was dressed nicely, wearing a top hat and gloves. "Are you going to a wedding?", I asked him. "No", he answered with pride, "I am going to see a member of the Jury!"

"Lucky devil! That you know a member of the Jury!", I exclaimed (even though I had already exhibited there twice, without knowing anybody).

Do you want to come with me?", my friend asked.

"Oui! But I do not have a top hat!", I replied.

"That is alright, come all the same.", he stated. We went straight to Guillemet's house on Clauzel Street (Paris).

Guillemet, a great strapping fellow received us in his workshop. He looked up and questioned me: "Are you making a painting, young man? You'll have to bring it to me so that I may see it."

"Yes", I said to him, "but it is two meters in height!", I exclaimed.

Guillemet wanted to see it anyway. A few days later it arrived, and he admired my work greatly. Swimming in the bliss, I sent my landscape to the Salon, but I did not win. I returned to see Guillemet in the following year, and he consulted with me. I became his pupil and it is to him that I owe it all.