Demi Lovato has been left ''heartbroken'' following the death of her great-grandfather.

The 'Cool for the Summer' singer has asked fans to pray for her great-grandmother after her beloved grandparent passed away aged 88.

Alongside a picture of the old man and her puppy Buddy, who passed away in July, she wrote on Instagram: ''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 in your prayers.(sic)''

Earlier this summer, the 23-year-old singer had asked fans to pray for her elderly relative as he was unwell.

Demi's dog Buddy - who she shared with boyfriend Wilmer Valderama - died in July after being attacked by a coyote in their backyard.

In the wake of Buddy's passing, the 'Skyscraper' singer took to her Twitter account to pay tribute to her canine pal, writing: ''We are absolutely heartbroken to be writing this but Wilmer and I are devastated to inform you that we lost our little angel Buddy last Sunday ... He was taken from us way too soon in a tragic accident and though I will never know why this had to happen, I do know that God only puts us through situations that we can handle so with that, together we our staying strong ... We will never forget our baby boy Buddy and his gentle loving spirit will live on in our hearts forever. RIP my tiniest little nightingale, Buddy ... I'll love you forever, I'll like you for always, as long as I'm living my baby you'll be... (sic)''