This morning, Grand Duke Henri had an arthroscopic surgery performed in his knee. The minor surgery had been planned for some time, it was performed to treat an injury of the meniscus in his right knee. As no complications arised he went back home in the afternoon hours.
In totally unrelated news I would like to refer you to Valentin Dupont's fabulous Royalement Blog who has posted more video footage of Hereditary Grand Duke Guillaume's interview with Place Royale.
Sources: RTL.lu, Tageblatt