Does the car remain the property of the questioner after the dispute that occurred with his grandfather and the latter's claim of its ownership, or is this considered a revocation of the gift, especially since the grandfather had begun to show signs of dementia and forgetfulness before his death, knowing that the car is registered in the questioner's name?

The general rule is that it is forbidden to revoke a gift, except in two cases: a gift given with the intention of recompense, where no recompense was provided, and a gift from a father to his child. This is based on the Prophet Muhammad's (peace be upon him) saying: "It is not lawful for a man to give a gift or a donation and then take it back, except for a father regarding what he gives to his child."

As for the grandfather, he does not have the right to revoke a gift after it has been taken possession of, according to the majority of jurists. Therefore, if the gift from the grandfather has been taken possession of, it becomes the property of the recipient, and the grandfather's attempt to revoke it has no effect.