This is a Eucharis, a perennial in the Amaryllis family. It's sometimes call the Amazon Lily, and resembles a narcissus (daffodil) with the striking central cup.
Lots of pics here: https://www.google.co.uk/search?q=Eucharis&source=lnms&tbm=isch&sa=X&ved=0CAcQ_AUoAW...
The Wikipedia article has instructions for propagating the plant, and if you do it in succession, you may be able to have blooming plants year round! Gorgeous plant--lucky you!