Is the prayer valid behind a latecomer?

The questioner:
May Allah reward you, Your Eminence, father. The questioner says: A person caught up with the imam in the 'Asr prayer after he had risen from the last rak'ah, and after the imam had said the taslim, he saw a latecomer who had caught up with that imam for three rak'ahs, so that latecomer completed his prayer by praying one rak'ah with him.

The Shaykh:
A man, what?

The questioner:
He says, may Allah reward you: A person caught up with the imam in the 'Asr prayer after he had risen from the last rak'ah, and after the imam had said the taslim, he saw a latecomer who had caught up with that imam for three rak'ahs, so that latecomer completed his prayer by praying one rak'ah with him. When he stood up to complete his own prayer, another latecomer came, so he completed his prayer by praying with that latecomer. What is the ruling on the prayer of each of the two latecomers?

The Shaykh:
This is all just an expansion, all of it is an expansion in this matter without fiqh and without knowledge. When a latecomer stands up, no one joins him. When a latecomer stands up, no one joins him, and he does not join anyone else; rather, he completes his prayer alone. As for this interweaving between prayers and imams, this is an expansion, but we do not say that his prayer is invalid. Rather, we say that this action should not be done in the future. Yes.