It's an oddball, one you probably will never see again. Strange feathers just happen sometimes.
@Ripshod Yours is very common, almost all my macaws have them and I'll get a picture in a bit. It's called an afterfeather.
It's a healthy bird thing when they are big.
Rosie had two super strange feathers. One that was a mute pink with a white vein and always grew in half deformed. She would molt it and it would grow the same again, sometimes split in two. Another feather that had no center shaft and it grew like hair. I would trim it like a hair cut. LOL