By now, most art history devotees know that on Christmas Eve in 1888, painter Vincent van Gogh allegedly took a razor to his left ear and chopped the appendage right off. Nearly none of them, however, know why.

A new theory from author Martin Bailey attempts to shed light on one of the darkest moments in the history of art. While researching for his book Studio of the South: Van Gogh in Provence, Bailey discovered that van Gogh’s act of self-mutilation occurred just after learning that his brother Theo had gotten engaged.

“Vincent feared that he would then ‘lose’ Theo, his closest companion,” Bailey explains in the book, per The New York Times. “He was equally worried that his brother might withdraw the financial support which had enabled him to devote his life to art. All this was threatened by the unexpected appearance of a fiancée.”

Bailey’s theory is largely based upon a letter, from Theo, delivered to Vincent just half a day before the ear incident occurred. The letter has since been lost, and there is no certain evidence of exactly what information the letter conveyed, but Bailey’s assembled enough information to reasonably infer that Theo’s letter announced his plans to wed.

“It’s a matter of putting all the clues together,” he told CNN. “We don’t have that letter, but in another one Van Gogh sends in January, he mentions receiving money from his brother on the 23rd of December.”

So we know that Vincent received a letter from Theo on Dec. 23, 1888, the day in question. Couple that with the fact that Theo’s bride-to-be, Johanna Bonger, received a telegram of congratulations from her older brother Henry on the same day.

It’s reasonable to deduce, Bailey reasons, that Henry was alerted to the wedding plans on Dec. 23, and Vincent, also a brother of one of the betrothed, would be alerted at the same time.

Once it’s established that this mysterious letter contained news of wedding bells, it’s not all that surprising that van Gogh, who was already struggling with mental illness, would be disturbed by news of his closest companion’s engagement. Van Gogh depended on his brother, both emotionally and financially, as he had yet to sell a single painting.

“It was fear that pulled the trigger and led to the breakdown,” Bailey told CNN. “Fear of being abandoned in both an emotional and financial way.”

Since there is no hard proof confirming Bailey’s theory, it has its skeptics, including Nienke Bakker, a curator of van Gogh paintings at the Van Gogh Museum in Amsterdam.

“It might have contained the news of Theo’s engagement, but this cannot be proven,” Ms. Bakker wrote in an email to The New York Times. “It is equally possible that Theo only informed Vincent of his marriage plans when he visited his brother in hospital — thus after the ear incident.”

Prior to Bailey’s hypothesis, the leading theory surrounding van Gogh’s psychotic episode posited that the artist suffered a psychotic break following a passionate fight with his close friend and fellow painter Paul Gauguin.

It is also possible, of course, that both the wedding and the argument contributed to van Gogh’s mental unease ― hence, the ear chopping.

We may never know for certain what led van Gogh to harm himself that fateful night, but the theories that continue to emerge sketch an increasingly detailed picture of the legendary, tortured life of an iconic artist, making his visceral paintings all the more haunting.