Pop star Demi Lovato is in mourning following the death of her great-grandfather.

The Skyscraper hitmaker first asked her fans to keep her 88-year-old great-grandfather in their prayers earlier this summer (15), taking to Instagram.com to reveal he was "not doing so well".

On Monday (28Sep15), Lovato, whose beloved pet pooch Buddy was killed in July (15), posted a photo of her Papa and late dog Buddy, writing the caption, "My two favorite Buddy's are now playing in Heaven. My heart is absolutely broken and I can't even begin to imagine a world without my Papa but I know one day we'll meet again and that's what keeps me going.

"I hate writing this... But RIP Papa... I miss you so much already. I love you. Please keep my Mimaw (great-grandmother) in your prayers."

In July (15), Lovato had a chance to spend time with her great-grandparents and posted a picture of the pair in separate beds and holding hands.

The singer wrote, "How precious is this??? Mimaw and Papa holding hands and still so in love.. It's so beautiful... Married over 50 years and he STILL looks at her this way.... I love them so much."