Hello Miranda
I don't think papayas can prove that hardy.
I'd bet you're talking about the Japanese aralia (fatsia japonica). It is commonly sold as a houseplant, and, yes, it has leaves that remind of papaya, somehow.
However, unlike papaya, it can prove fairly hardy, maybe even in a sheltered spot in belgium.
That's my only guess, I can't really see any other candidate.
Regards
Rajesh