Queen Marie of Romania

Via Alabaster.  I was unable to find an explanation as to whether the headdress is part of some ceremony of state, or whether this is stage/costume/revelry related.  A TinEye reverse image search didn't help.  Biography here.

Addendum:  A hat tip to reader Unknown ND Martin for finding the definitive answer: "Diana Mandache originally published the picture in her book about Queen Marie and in correspondence noted that (then) Princess Marie was dressed as the Sun for a fancy ball."