Jessi Combs, 36, died Wednesday afternoon while attempting to break her own land-speed record in a desert in southern Oregon.
Combs, a former race car driver and TV personality, was attempting to reach speeds of 512 MPH.
"She was truly my unicorn and I enjoyed every single minute that I had with her. She was the most amazing spirit that I have ever or will ever know," her boyfriend Terry Madden, who was on the scene of the crash wrote in an Instagram post. "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."
Combs was known as the "fastest woman on four wheels" and had appeared on the television shows Xtreme 4x4 and Overhaulin in addition to Mythbusters.