Is it necessary to inform a friend about the truth of a prank after more than three months of the perpetrator's denial?

Joking with lies, backbiting, or tale-bearing is impermissible, and whoever commits such acts must offer sincere repentance. One could have used tawriyah (double entendre) and ma'areedh (indirect speech) to avoid lying. Informing a friend depends on whether there is a benefit or harm in doing so.