The cause of death of Grammy-winner Natalie Cole has been revealed: a rare lung disease that ultimately caused her to die of heart failure — and it’s a disease that had long been attacking the legendary singer’s body due to years of drug use.

Cole, known for her 1991 album “Unforgettable … With Love” as well as being the daughter of legendary singer Nat “King” Cole, passed away on Dec. 31 at a hospital in Los Angeles at the age of 65, according to a Fox News report.

She had undergone a kidney transplant back in May of 2009 due to drug problems and hepatitis she had battled with in her life. Cole had been diagnosed with pulmonary arterial hypertension after the transplant. This condition results in symptoms such as dizziness, shortness of breath, and chest pain.

Cole acknowledged in a 2000 autobiography that she had used drugs such as heroin and crack cocaine, and she also battle alcohol addiction, leading to six-month rehab stint in 1983. She said intravenous drug use was the cause of her hepatitis C diagnosis in 2008.

Despite problems with her health, Cole continued to perform at many concerts around the world. Ultimately, however, her heart gave out as commonly happens with this disorder, which is a progressive disease.

According to a statement obtained by People, Cole’s family indicated that she suffered from a “very serious and progressive disorder.” She “responded well to PAH-specific agents over many years, during which she performed many concerts world-wide, but eventually succumbed to intractable right heart failure, an outcome that unfortunately commonly occurs in this progressive disorder, despite modern therapies.”

Cole sold 14 million copies of her “Unforgettable” album and won six Grammy Awards. The album was a tribute to her famous father, and included reworked versions of songs such as “That Sunday That Summer,” “Too Young” and “Mona Lisa.”

Cole first rose to fame in the mid 1970s with hits like “This Will Be,” “Our Love,” and “Inseperable.” It was after this time that she began to get heavily involved in drugs before reemerging in 1987 with the album Everlasting, and then the Unforgettable album in 1991. Cole has sold more than 30 million records worldwide.