Anita Pallenberg, an actress and model who had been the girlfriend of both Keith Richards and Brian Jones of the Rolling Stones, has died of unknown causes. She was 73.

The news was made public by Stella Schnabel, the daughter of painter and director Julian Schnabel. "I have never met a woman quite like you Anita," she wrote on Instagram. "I don't think there is anybody in this universe like you. No one has ever understood me so well. You showed about life and myself and how to grow and become and exist with it all. I was a little girl thinking I was big but I became a woman through knowing you. The secret lyrical you. My best friend. The greatest woman I have ever known. Thank you for the most important lessons - because they are ever changing and definitive. Like you. We are all singing for you, how you liked it. Go in peace my Roman mother, you will always be in my heart."

Born in Rome on Jan. 25, 1944 to German parents, a 2008 profile in The Guardian says that she was expelled from boarding school at age 16, after which she was involved in the art scenes, first in Rome and then New York, before moving to Paris and became a model.

In 1965, she and a friend attended a Rolling Stones concert in Munich, at which she got backstage and met Brian Jones. "My first impression was of a woman who was very strong," wrote Keith Richards in his autobiography, Life. "I was right about that. Also an extremely bright woman, that's one of the reasons she sparked me. Let alone that she was so entertaining and such a great beauty to look at. Very funny. Cosmopolitan beyond anyone I'd come across. She spoke three languages. She'd been here, she'd been there. It was very exotic, to me."

However, her time with Jones corresponded with his descent into drug addiction, and he would occasionally beat Pallenberg and Richards, who was spending a lot of time with the two of them, drew closer to Anita. In March 1967, Jones, Pallenberg, Richards and two others had planned a drive to Morocco. However, Jones dropped out after the first night due to pneumonia, and by the time the vacation was over, Pallenberg and Richards were a couple.

In 1970, Pallenberg starred with Mick Jagger in Performance. In Life, Richards said that she and Jagger had an affair on the set, a charge Pallenberg repeatedly denied. The guitarist blamed writer-co-director Donald Cammell with facilitating it. But the couple had much bigger problems looming; they had started using heroin.

The couple were arrested upon landing in Toronto in 1977 when a spoon was discovered on Pallenberg. A stint in rehab for both followed, but The Guardian said that "it worked for him, but not for her."

Two years later, while Richards was recording with the Stones, Scott Cantrell, a 17-year-old with whom Pallenberg was having an affair, shot himself in their bedroom in South Salem, N.Y. It was rumored that they were playing Russian roulette, but Pallenberg was eventually cleared. "I didn't feel anything," she told The Guardian. "That's one of the wonders of drugs and drink." Pallenberg and Richards broke up shortly thereafter, and it wasn't until 1987 that she got clean.

Later in life, she studied fashion design and resumed her acting career in the late '90s.

Rocker Deaths: Artists We Lost in 2017

More From Ultimate Classic Rock