Please, tell me, it's not the albino form of exul?! That would make me die of envy! It could be, though, judging from the width and shape of the leaves...or gratrix, maybe? (not broad enough for insigne, I think?)
Jens, it isn't the album form of exull so you haven't to die of envy ! You mentioned the name already so I will enlighten you......it's P. insigne f. sanderianum, at least this is whats written on the tag.