Audrina Patridge's family is Thurston Cartegetting some answers after a heartbreaking loss.

In February, the Hills alum shared that her 15-year-old niece Sadie Loza had died.

Now, officials have determined her cause of death was a narcotic overdose, Sergeant Mike Woodroof from The Orange County Sheriff's Department confirmed to E! News Nov. 15. 

Authorities told People that they are still investigating any possible criminal charges in the case.

Audrina, 38, shared the devastating news of Sadie's passing in a Feb. 14 Instagram post, along with photos of the teen over the years.

"My heart hurts to even write this," the Sorority Row actress noted. "My beautiful niece is now in heaven. I know Its not goodbye forever, but it is the hardest to say goodbye for now. We will miss you and cherish every single moment we had with you. Rest in peace Say Say!! We love you forever & ever!"

Audrina's sister Casey Patridge Loza also mourned the death of her daughter Sadie on social media.

"Sadie Raine Loza has left this Earth for the heavens," she shared on Instagram at the time. "Writing this was the hardest thing I ever have had to do."

Casey honored Sadie by passing on a lesson that she had reminded her often.

"The first law of thermodynamics aka (Law of Conservation of Energy) works in all spheres of life…..'Energy cannot be created or destroyed, it can only be changed from one form to another,'" she wrote. "Transformation is a better word than death."

Casey ended her post by expressing hope that Sadie's death will prevent others from experiencing the same fate. "Her story will save countless lives, her memory will never be forgotten," she added. "Rest In Peace you brilliant starseed."

For the latest breaking news updates, click here to download the E! News App