I had it the other way, without me knowing…
She knew I liked her to try another guy, but she always opposed it, then one day while I was at work and she was at school she called me and told me she is coming to my office, I wondered why the urgency. After 5 min she came and told me “you know about that idea of your…” I said “yes”, and she just raised her shirt and all of her belly was still with sperm all over…
I was thinking she is joking since we never did it before, but then she told me one guy from her university asked her for some homework help… and she went for it…