Whitney Houston died of a lethal combination of Valium, Xanax and alcohol, sources close to the Los Angeles investigation told RadarOnline.com.

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"Whitney had taken Valium, Xanax, and alcohol, which led to her death. The coroner is waiting on final toxicology results to determine which one of the three was the major contributing factor of her demise," the insider said.

"The coroner will be closely examining Whitney's blood-alcohol content at the time she died as well. The sedatives and alcohol will almost certainly be the cause of death, and not drowning. Her heart stopped beating because her respiratory system was suppressed because of the anti-anxiety meds, and combined with the booze it probably happened very quickly before she was found partially submerged in the bathtub."

The 48-year-old Grammy Award-winning recording star, who had long battled addictions to drugs and alcohol, died Feb. 11 in her bathtub at the Beverly Hilton hotel.

She was buried Sunday in her native New Jersey.