@Christopher McGovern I haven't read the novel in a while but I'm pretty sure that Eva is a former noble of the same country from which MC's parents hailed from originally. MC's father was a noble, turned adventurer after a massive demon incursion, and his mom was a high priestess also turned adventurer for the same reason. They then isekai'd into our world and raised a family there. AFAIK none of them were royalty, just counts or something like that. They likely saw eachother at noble events, hence why she was familiar with them.
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