I'm not sure whether the 'medieval times' is accurate. The lion had a historical range which covered the Iberian peninsula, Italy and Greece, but they had gone from Greece by about 100BC, from Italy by 1AD, and from the Balkans by 100AD. The last remnants were in the Caucasus mountains up to 1000AD (possibly), and that's barely still Europe. Turkey still had lions up until the C19, but that's definitely not Europe.
Lions were kept as captive animals to the royals - the English kings had lions in their menageries, so did the Holy Roman Emperor and several other monarchs. The Lion was very much known about, popular in legends and bestiaries, but it was not indigenous fauna.
For my taste, I'd stick closer to cannon on the 'acceptability' of domesticated animals as heartbeasts. I would then also use the opportunity to include some kind of flaw for the social stigma within the house into the template.