The 'Problem' singer flew straight to her native Boca Raton in Florida to be by his side in hospital after performing at Macy's Fourth of July Fireworks Spectacular, reported Contactmusic.
"Love you grandps I need you please pull through (sic)," she tweeted.
"Thank you for the prayers. My loves u are so powerful... You are in my heart. I am going to try my best to put my selfishness aside thru this... As much as I want grandps here with me.. I should just want him to be comfortable," she added.