This was tagged Paphiopedilum Sumurum, but the International Orchid Registry doesn't have a plant by that name, and I think we all know how seriously to take orchid tags by now. The IOR does know of a Sumurun, though, which is what I'm assuming this is, and there's sort of confirmation at the Eastern Iowa Orchid Society newsletter from March 2014, which shows a very similar-looking flower on page 5, identified as Sumurun 'Pearl,' presumably the same specimen.
Further confirmation: among many other very interesting plants photographed at the Montreal Botanical Garden,1 this page includes a Sumurun 'Boholt' that resembles this flower, which is the best I could do for confirmation.
Paphiopedilum Sumurun = Paphiopedilum Boltonii x Paphiopedilum Christopher (Ref.)
I was unable to find photos of either parent, when I looked back in March. I did find a half-sibling (on the Boltonii side) that is also mostly white with some faint spotting, though I apparently didn't save the link so I can't show it to you.