Got here too late, I could have told you the name as I have had it for years, mine has been in a small pot forever, poor thing, but it sure doesn't mind one bit. It gets morning sun through the window in my dining room and blooms regularly. Sometimes I forget to water it and it gets bone dry, still doesn't care. It's one tough begonia. I need to add some updated photos soon, plus I bet it would be so happy if I repotted it.
Stained Glass Begonia (Begonia 'Cathedral')