Countess Stéphanie de Lannoy, youngest child of Count Philippe de Lannoy and his wife Alix della Faille de Leverghem. Count Philippe is the eldest son of the late Count Paul de Lannoy and Princess Beatrix de Ligne. Another member of the de Lannoy family, Countess Minthia is married to Prince Lamoral de Ligne, youngest son of Princess Alix of Luxembourg.
Prince Lamoral and Grand Duke Henri are first cousins.
This is all pure specualation on the part of a poster at the Royaute newsgroup.