If the imam adds a fifth rak'ah by mistake, does the one who joined late count it?

Question:
May Allah reward you, Honorable Shaykh. The questioner says: If a person joined the prayer late, missing one rak'ah, for example in the 'Asr prayer, and he entered with the imam and prayed with him, but the imam forgot and added a rak'ah, so the latecomer had four and the imam had five.

Answer:
No, the extra rak'ah is not counted. He stands up and completes his rak'ah, and the extra one is not counted because it is not part of the prayer. Yes.