The 23-year-old singer asked her fans to keep her grandfather, who was 88 when he passed away recently, in their prayers during this hard time.
"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," the pop rocker captioned the photo of her grandfather.
The "Cool for the Summer" singer received tanks of support from her fans, who asked her to "stay strong".