Audrina Patridge is grieving the loss of her niece Sadie Loza, who passed away at the age of 15.

The 37-year-old reality star took to Instagram on Tuesday to share an emotional tribute to Sadie, who was the daughter of her sister Casey Loza.

"My heart hurts to even write this," "The Hills "alum wrote in the caption of her post.

She continued, "My beautiful niece is now in heaven. I know Its not goodbye forever, but it is the hardest to say goodbye for now."

Audrina Patridge is mourning the death of her niece Sadie Loza, who died at the age of 15.

Audrina Patridge is mourning the death of her niece Sadie Loza, who died at the age of 15. (Audrina Patridge Instagram/Getty)

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"We will miss you and cherish every single moment we had with you. Rest in peace Say Say!! We love you forever & ever!"

The television personality shared a slideshow of photos featuring Sadie over the years, including several photos of her as a child, a family group photo and an image of her niece as a teenager. 

In one photo, Patridge and Sadie beamed as they posed together for a selfie. The two were seen dancing at Patridge's wedding in another image. The "Dancing with the Stars" alum married Corey Bohan in November 2016, but they went on to divorce in 2018.

The model also included a video in which she was seen smiling with her sister and her niece with their arms around each other's shoulders. At the end of the clip, Loza gave her daughter a peck on the cheek.

Patridge's post was quickly met with supportive comments from her friends including several of her "The Hills: New Beginnings" co-stars.

"So so sorry for your loss Audrina. This is heartbreaking. Sending love to you and the family," Brody Jenner wrote.

Kaitlynn Carter commented, "oh my goodness, I’m so sorry love you," along with a crying face emoji.

"Omgggg this kills me," Kristin Cavallari wrote.

"rest in paradise..," Frankie Delgado wrote in the comments, along with emojis of prayer hands and a crying face.

"I am so sorry for your loss," Paris Hilton wrote with a tear-eyed emoji and a broken heart emoji.

On Tuesday, Loza announced Sadie's death with a heartfelt Instagram post that featured a recent photo of her daughter.

"Sadie Raine Loza has left this Earth for the heavens," Loza wrote in the caption.

audrina patridge niece

"The Hills" alum shared a tribute to Sadie on Instagram. (Audrina Patridge Instagram)

She continued, "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"."

"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."

Loza appeared on episodes of "The Hills" and "The Hills: New Beginnings." She and her husband Kyle were also featured on Patridge's 2011 VH1 reality series "Audrina."

Kyle, who was Sadie's stepfather, shared a tribute to the late teenager to Instagram on Wednesday.

"Baby girl- I will carry your memory with me until I see you again," he wrote in the caption, along with a photo of Sadie.

"I can't stop thinking about you. I'll never stop loving you and I would do anything to laugh with you one more time. You were my first Love. NSD."

He signed the tribute "Dad" with along with a heart emoji.  

Sadie's cause of death has not been publicly disclosed.

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Sadie celebrated her 15th birthday less than two weeks before her death. Loza shared a video of her daughter holding a cake and blowing out candles at her birthday party.

"i cant believe youre 15," she wrote. "it feels like the years flew by and we still have so many more adventures to go on! aliens in sedona, portals, learning to drive in the desert hahah i love you so much my little clone."

She continued, "youre so beautiful, kind, smart and funny!! that dryyy af british humor tho. im so proud to be your mom and i cannot wait to see the insane ancient civilization architecture you’re going to construct someday. i love you so so much my sadie raine."

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