[2] Through Theo, he knew Vincent van Gogh, who called him "André" in letters.

[3] In a letter that Bonger wrote to his parents on March 31, 1885, he describes Theo van Gogh as having received unexpected news the prior week that his father had died due to a "stroke of apoplexy" after having received a letter the previous day that he was in perfect health.

In several letters over the remainder of the year, Bonger comments on a growing appreciation for and friendship with Theo.

Andries believed that his younger sister should not have sole say about what became of these remnants of her marriage and attempted to exert his influence over her.

Around this time, Bonger started collecting art, especially works by Odilon Redon and Émile Bernard, who were his friends.