In the documentary “Mystify: Michael Hutchence” — which premiered Thursday at the SVA Theater as part of the Tribeca Film Festival — the late INXS rocker’s ex, Helena Christensen, speaks for the first time about the accident and subsequent brain damage that led to his downward spiral.

The Danish supermodel reveals that the depression that ultimately led a 37-year-old Hutchence to commit suicide by hanging himself in 1997 was triggered five years earlier, when he was assaulted by a taxi driver while the couple were bicycling together in Copenhagen. Christensen, who was in a relationship with the Australian singer from 1991 to 1995, recounts how the attack caused Hutchence to fall back and hit his head on the ground.

With blood coming from his ears, Hutchence went to the hospital, but he insisted on leaving without proper treatment. Instead, he went back to Christensen’s apartment, where he hid away, barely eating and lashing out at her. Finally, Hutchence went to seek medical attention and discovered that he had suffered brain damage that caused him to permanently lose his senses of smell and taste.

While Hutchence kept his brain damage a secret, the documentary — directed by his friend and INXS music-video director Richard Lowenstein (“Need You Tonight”) — depicts how, sadly, he was never the same after that.

“Helena had never spoken about that accident,” Lowenstein said to the audience after the screening. “It’s never been really looked at in how profound that was in changing Michael’s life and what happened at the end. She kept quiet for very personal reasons…It was kind of amazing to get that firsthand account of it.”

The film — which also features interviews and footage with Hutchence’s friend Bono and another famous ex, Kylie Minogue — also shows how his post-Christensen relationship with the late British TV personality Paula Yates took a toll on him because of an ugly, media-crazy custody battle that she had with her ex, Bob Geldof.

In fact, after Yates died from an accidental heroin overdose in 2000, Geldof was awarded custody of Tiger Lily, Hutchence’s daughter with Yates, who is now a 22-year-old model.