Hilchos Lashon Hara, chapter 2, section 13

Someone told a friend, in front of three people, details about their own business, trade, and the like. Usually such details may not be passed on, because it might cause harm or pain to the one who shared them.

But since they said it in front of three people, it shows they are not worried about this. So the listener is allowed, even from the start, to tell others – as long as the person did not show that they mind.