It's an old leaf. Those kinds of leaves almost always die back first.
I don't know how often you water, but it could use a bit more water.
Btw, if you want your Miltassia to look nicer, I highly recommend pointing the new growths towards the light source. You don't have to, but it's just a little aesthetic tip.
Since your Miltassia is an intergeneric hybrid of the natural genus Miltonia
, the proper way to write your orchid's name is M
helob to denote that it is a hybrid. In fact, a few people might get up in arms and say, "Why are you being the orchid name police?", either seriously or in a half joking manner. Right now, it's easy to just dismiss this taxonomy rule because it's pretty clear to people that the name is the name of a hybrid. Wait until you start finding hybrids with species looking names and I think you're likely to gonna want to obey those taxonomy rules by correctly writing those names out. It's going to be very difficult, (or rather, I should say, extremely confusing), to get the proper information down if people throw these rules out the window.