One of the annual foreign royal guests at the Sultan of Brunei's big birthday bash is Princess Basma of Jordan, the younger sister of the late King Hussein and the aunt of the current king, Abdullah II. She's the woman all the way on the left of this photo.
Basma's tiara is a really interesting diamond piece -- from a distance, it almost looks like a floral tiara, but up close, it's more of an intricate abstract pattern of circles and swirls, with a top element that almost looks like the Prince of Wales feather emblem. It's stunning! (And Basma has grown her hair out a bit in recent years, which sets of the tiara really well. Love it!)