'The Hills' Star Audrina Patridge Mourns Death of Her 15-Year-Old Niece

Audrina Patridge is mourning the death of her niece. The Hills alum shared the heartbreaking news Tuesday that her niece, Sadie Raine Loza, recently passed away one week after her 15th birthday. Sadie's passing was first confirmed by her mother, Patridge's sister Casey Loza. Her cause of death was not disclosed.

On Instagram, Patridge paid tribute to Sadie by sharing a gallery of images of the teen and their family. She shared in the caption, "My heart hurts to even write this. My beautiful niece is now in heaven." The reality TV star continued, "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!"

Patridge's heartbreaking post was immediately met with an outpouring of support from her The Hill co-stars. Brody Jenner wrote, "So so sorry for your loss Audrina. This is heartbreaking. Sending love to you and the family," with Kristin Cavallari commenting, "Omgggg this kills me." The Bachelor's Kaitlyn Bristowe replied, "I can't even imagine that sort of pain. I'm so sorry." Actress Rachel Bilson told the star, "Audrina! I'm so so sorry," adding that she was "sending all the love and light to you and your family."

At this time, details surrounding Sadie's tragic passing remain unclear. Shortly before Patridge paid tribute to her niece on Tuesday, her sister, Sadie's mother, Casey Loza, confirmed her daughter's passing, sharing on social media, "Sadie Raine Loza has left this Earth for the heavens." Loza said, "Writing this was the hardest thing I ever have had to do."

"Not knowing the right words I'll leave you with this, Sadie liked to remind me that 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 continued. "Transformation is a better word than death. Her story will save countless lives, her memory will never be forgotten. Rest In Peace you brilliant starseed. You're with your creator. We will miss you dearly. I love you."

Sadie's passing came just a week after the family celebrated her 15th birthday, with Loza writing at the time, "i cant believe youre 15. it feels like the years flew by and we still have so many more adventures to go on!" In addition to Casey, Patridge has another sister, Samantha Patridge, as well as a brother, Mark Patridge.