Cousin of the late Whitney Houston, Dionne Warwick has opened up about what she believes really killed her superstar relative on Feb. 11, AOL Music reports. As family, friends and fans await the results of toxicology tests and Whitney's official cause of death to be released, the grief-stricken Warwick has already come to her own conclusions about her cousin's sudden passing.

The 71-year-old singer-actress told ET in an interview that airs tonight (March 13), "You know, in all honesty, I think she had a heart attack, that's what I think happened to her." When asked about Whitney's drug use playing a possible role in her death, Warwick insisted, "I don't know if it's that or not. I think her heart just gave out."

Dionne also described the emotions she felt as she accompanied Houston's body aboard the plane that transported her from Los Angeles back to her native New Jersey for Whitney's funeral. "It was a combination of things, stories, laughter, tears. All the emotions that you feel when somebody very near to you passes," she admitted.

Dionne, whose late mother Lee Drinkard Warwick was the sister of Whitney's mother Cissy Houston, previously revealed that she spoke with Whitney on the morning of her tragic death. The troubled singer talked to Warwick over the phone about record label executive Clive Davis' Grammy party, where she was scheduled to appear that night. "She said, 'You're here, aren't you? You're coming to the party, aren't you?' I said, 'Yeah, I'm going to be there' and she said, 'Thank you, I want you to be here. You've got to be here for me,'" Warwick recounted during an interview on 'Good Morning America' last week (March 8).

For more on the exclusive interview with Warwick, visit ET.

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