This is supposed to be a Cernuum lily. Does anyone know if they sometimes come double? I actually think there were almost three layers of petals/sepals, just one is so far turned back and curled inward toward itself that you can't see it/them.
I suppose 'polytepal' might be the more correct term, though it looks like some of the reproductive parts are fused. No matter, it is just an oddity rather than anything worrisome. Fun to watch for ~ :)