The 29-year-old singer shared the news over the weekend.
Demi Lovato is mourning the loss of their grandmother, Sue Hart. Sue was the mother of Demi's mom, Dianna De La Garza, who announced the news on social media.
"My heart is broken today but I know you’re flying with the angels now... give Daddy a kiss on the cheek for me and tell him I love him," Dianna captioned a photo of herself with her mother. "Y’all have lots to catch up on... I love you forever, my sweet funny beautiful Mama ❤️ I’ll see you again one day...💔🙏🏻💔"
Demi commented on their mom's post, "I love you momma so much."
On their Instagram Stories, Demi posted several photos with their grandmother, writing, "This hurts so f**king bad.. I'll miss you and our phone calls and I love you so much Grandma. I miss you already @merryharts."
The 29-year-old singer also shared a photo with their siblings, mom, Sue, and late great-grandmother, Mimaw, who died in May 2016.
"Four generations in one picture. She's with Mimaw now," Demi wrote.
The "Anyone" singer said their grandmother "saved three lives donating her organs," adding, "She's a hero."