Shuli Rand – Defamation

Hello Rabbi!
An investigation was recently published into the marital life of singer Shuli Rand and the alleged abuse he suffered from his wife.
The article was broadcast after years of silence on his part regarding severe slander against him and came as his response to these slanders.
I wanted to ask whether, in your opinion, it is permissible for a person who is being slandered to defend himself and tell the truth, even if he must, for this purpose, slander those who are slandering him? And if you believe that it is permissible, is it appropriate for me, as a person on the side, to allow him to express himself to me and tell me the truth in order to allow him to defend himself. Or is it that since I am ultimately not a part of the matter, this is considered slander to me and I should avoid hearing the truth.
Of course, Shuli’s story is just an example. It often happens that a person is slandered and forced to tell at least his relatives the ugly truth…
Thank you very much!