Thanks Camille,
I guessed it was quite possible for two fans to flower together... but was
really suprised to find two buds on the one spike.
The two buds formed together, one of them upside down with it's underside upwards and pressed against the underside of the first. The upwards one was always somewhat bigger than the lower. About a week before the upper one started to open (which took a long time) the lower one started to turn. I wish I had taken pictures of the late stage of the buds now, but it doesn't look like I did. By the time I took pictures of the first flower, the lower bud had already turned over.
It's not like the sequential bloomers (like Pinocchio) which form new buds, one after the other. This was definately two forming together.
The second spike looked like it could have formed two as well, with a bud sheath for a second bud, but no second bud ever formed on that one.