Late in the evening of Dec. 23, 1888, Vincent van Gogh mutilated his ear. That insane act is the most celebrated case of artistic temperament. But why he did he have his crisis then?

Journalist and Van Gogh scholar Martin Bailey has published an intriguing new clue.

The traditional explanation is that Van Gogh's fraught relationship with Gauguin, who had been sharing his small house in Arles, France, for the previous two months, was the trigger; in particular, Gauguin announced he was leaving.

But Bailey, writing in the Art Newspaper, has found evidence pointing in a different direction. It's contained in the Van Gogh painting "Still Life With a Plate of Onions."

Shortly before Christmas, Vincent's brother, Theo, asked a Dutch woman, Jo Bonger, to marry him. In surviving letters, Theo first mentions talking about his engagement with his brother after the ear incident, when Vincent was recovering in the hospital. It now seems that Vincent might have been informed by mail a few days earlier and that Theo's happy news helped, at least, to push him over the edge.

"Still Life With a Plate of Onions" was one of the first pictures he painted on leaving the hospital on Jan. 7, 1889. It features a detailed representation of an envelope addressed in Theo's handwriting.

Microscopic examination reveals that this probably arrived on the morning of that fateful day, Dec. 23. It was posted near Theo's Paris apartment, and the postmark was one used immediately before the New Year. While the actual letter, like most of Theo's, was lost or thrown away by the untidy Vincent, it might have contained news of the engagement. Bailey suggests that Van Gogh painted this missive with such precision because it was ominously significant.

There were reasons why Vincent might have found his brother's romance threatening. Financially and emotionally, he was dependent on Theo. A wife and family might have made it impossible for Theo to continue to support his unsuccessful painter-brother. And it's true that, as Bailey points out, Van Gogh's first recorded remark about Theo's glad tidings doesn't sound ecstatic. He told Theo that he approved of his plans, "but that marriage ought not to be regarded as the main object in life."

On the other hand, Van Gogh's other responses to Theo's new family life were positive. One of the most joyful of all his paintings, "Branches With Almond Blossom," was a celebration of the birth of Theo and Jo's child in early 1890.

Also, that still life seems to be about renewed health and hope, not despair -- the sprouting onions might be a symbol of returning life, and it contains a self-help medical manual. So if Vincent included the letter for a special reason, it might have been because it was a harbinger of good news, not bad.

Still, Van Gogh's failure to marry or sustain a sexual relationship was one of the miseries that gnawed at him. At a time when he was already in turmoil, Theo's new love might have made him feel even more of an isolated failure. Bailey's discovery adds a fresh twist to one of the great art mysteries.