What does the one who joins the prayer late do if the imam prostrates for forgetfulness in a part of the prayer that the latecomer did not catch?

Question:
May Allah reward you, Honorable Shaykh. This questioner says: If one catches up with the imam in the last rak'ah, and the imam has made a mistake in his prayer that requires him to perform the prostration for forgetfulness after the prayer, the question is: Does the latecomer complete his prayer, or does he prostrate for forgetfulness with the imam and then complete his prayer?

Answer:
It is not permissible for him to stand up to make up what he missed until he has prostrated with the imam. If the imam prostrates for forgetfulness, even after the taslim, the latecomer does not say the taslim with the imam. If the imam prostrates after the taslim, he must prostrate with him and not stand up. When the imam finishes the prostration and rises from the second prostration, the ma'mum stands up to make up what he missed, unless the ma'mum has already stood up and is fully upright; in that case, he does not go back. However, if the imam prostrates before the ma'mum is fully upright, he goes back and prostrates with him. Yes.