The ruling on a follower who missed a rak'ah and the imam stood for a fifth

Question:
A follower caught up with the imam in the second rak'ah, but the imam stood for the fifth without being alerted, and the follower was uncertain. When the imam finished the fifth, he was alerted, so he prostrated the prostrations for forgetfulness. While he was prostrating, the follower stood up to make up the missed rak'ah?

Answer:
He prostrates for forgetfulness after making up what is due from him, if he did not prostrate with the imam.
Q: Before the taslim or after it?
A: He prostrates before the taslim; this is what is best.