Stranger talking through Minecraft Server?

Ok, so I encountered something weird when I was playing alone on my fiancé's minecraft server. Someone suddenly wrote "hi" to me through the server console, and I thought it was my fiancé playing a trick on me or something, because it wasn't his usual style of writing. Then the "person" proceeded to tell me that "she" was going to become a mum and asked me if I could donate money to her and her child. That's when I clearly understood that this "person" was not my fiancé, since he was sleeping at that moment. Does anyone have any idea what it could be? I'm thinking that it might be a virus, but can a virus actually access the server console and control it? Or could it be that someone has taken control over his computer?
Any serious answer would be highly appreciated, since this is something I do not take lightly considering he has a fair amount of nudes of me on his computer and I don't want them to be spread across the internet…

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