MythBusters star Jessi Combs is dead at the age of 39.

The professional racer passed away on Tuesday, August 27, in a “horrific accident” after attempting to break her own speed record, her team member and partner Terry Madden confirmed on August 28.

According to Oregon news station KTVZ, the Discovery Channel personality died in a fatal crash in the Alvort desert in southeast Oregon after trying to surpass her own land speed record in a jet-powered vehicle. The station said that the Harney County Sheriff’s Office and the Bureau of Land Management are investigating the incident.

Combs, who was born in Rapid City, South Dakota, was the cohost of Spike TV’s Xtreme 4×4, in which she and other car experts modified vehicles to turn them into off-road-oriented rigs. She also appeared on TLC’s Overhaulin’, Discovery Channel’s MythBusters and Science Channel’s How to Build… Everything.

In his Instagram tribute to her, Madden described Combs as the “most amazing spirit” he had ever known.

“I have never loved or been loved by anyone as much as this amazing woman @thejessicombs,” he captioned a slideshow of videos and photos of them together. “She was truly my unicorn and I enjoyed every single minute that I had with her.”

He continued, “Unfortunately we lost her yesterday in a horrific accident, I was the first one there and trust me we did everything humanly possible to save her!!”

Madden explained that, before Combs’ death, she told him to “do good” with her legacy if her attempt ended in tragedy. He said that the two were working on a documentary, which he will finish in her honor, and that proceeds from the film will go toward Combs’ foundation, which he and her family will announce soon.

“The world will know the truth and her foundation will use those funds to do amazing things in this world and make her legacy live on properly,” he wrote.

He added, “She dedicated her life to helping support others dreams and I promise I will continue that.”

Combs appeared on 12 episodes on season 7 of MythBusters while regular castmember Kari Byron was on maternity leave. After the news of the racer’s death, Byron took to Twitter to pay tribute to the late star.

“So sad to hear about Jessi. She was a badass. Always pushing limits. Sending smiles into the universe for her,” Byron tweeted.

Discovery Channel told Us Weekly in a statement, “The Discovery and MotorTrend family is deeply saddened to learn of the tragic passing of Jessi Combs. She was a friend and colleague, an icon in the industry, and an undeniable force of nature who left an indelible mark on the car world. Our thoughts are with her family and loved ones.”

The Spike TV personality earned the title of “Fastest Woman on Four Wheels” after driving a record 440 mph in 2016, according to KTVZ.