Royal watchers are eagerly awaiting the Omani state banquet at Windsor Castle on Tuesday, October 20, but on Monday night, the Danish royals celebrated their own state visit from the president of Vietnam. Although Queen Mary didn't go for an overt diplomatic nod with her rich blue outfit, Vietnam is a notable producer of sapphires, and the Danish queen took the opportunity to debut a sparkling tiara that dates back to the late 1800s.

Mary skipped the red and yellow of the Vietnamese flag in favor of a shimmery off-the-shoulder top by Jesper Høvring that she's had in her closet since 2014, pairing it with a navy velvet maxi skirt.…