The family of Natalie Cole released a statement to ET on Thursday revealing the singer's cause of death: Idiopathic pulmonary arterial hypertension.
"This is a very serious and progressive disorder in which the small blood vessels of the lungs are markedly narrowed or obstructed," the family's statement read, adding that Cole had been diagnosed with IPAH five years ago after a successful kidney transplant.
WATCH: Natalie Cole Dead at 65: Dionne Warwick, Questlove, Cher, Gigi Hadid and More Share Touching Tributes
"She responded well to PAH-specific agents over many years, during which she performed many concerts worldwide," the statement continued. "[She] eventually succumbed to intractable right heart failure, an outcome that unfortunately commonly occurs in this progressive disorder, despite modern therapies."
Cole died at Ceders-Sinai Medical Center in Los Angeles on New Year's Eve at the age of 65. After her death, friends and fans took to social media to express their grief over the loss of the legendary singer.
RELATED: Smokey Robinson Remembers Natalie Cole
Music legend and Cole's close friend, Smokey Robinson, spoke with ET about her legacy, calling the "Our Love" singer "one of our greatest musical icons."
Cole's sisters Timolin and Casey also opened up with ET about their last days with Cole before her death, who were glad they got the chance to spend Christmas Eve with their sister days before she died.
WATCH: Natalie Cole's Sisters Open Up About Their Last Days With the Legendary Singer
"We were very blessed and thankful to spend that very special day with her that she loved. It was her favorite time of year."
Watch the video below to her more from Cole's sisters about her final days.