Here's a right royal event: Princess Michael of Kent, attending the reinterrment of the remains of famous French royal mistress Diane de Poitiers, who also happens to be one of Princess Michael's ancestors. (Marie-Christine is also descended from Catherine de Medici, the wife of King Henri II -- the same king who kept Diane as a mistress! What a royal tangle.)
But her ancestry likely isn't the only reason Princess Michael is attending this reinterrment; she has also written a book, The Serpent and the Moon, about both Catherine and Diane. Diane's remains were moved to a mass grave during the French Revolution, and this ceremony is marking their return to the chapel at Chateau d'Anet, Diane's former home.
Marie-Christine has chosen some rather dramatic headgear here: a string of pearls, draping like a headband across her forehead. I suppose this is a nod to Diane, who wears pearls in several of her portraits. It's also pretty costumey, but compared to the get-up sported by the current owner of Chateau d'Anet (he's on the right), it's pretty mild!