The pop star took to Twitter.com to ask fans to pray for his grandpa Douglas, who is currently fighting for his life, before taking to the stage in the Off-Broadway production.
Carter tweeted, "I dedicate this show tonight to my beloved grand father Douglas Spaulding, he is in his last hours right now. I'm devastated."
The 25 year old also posted photos of himself with his grandfather, before adding, "You're everything I want to be. Brilliant actor, brilliant writer, Shakespeare scholar & genealogist. Grandpa, I love you, I promise I will make you proud of me."