It can hardly be a great surprise to anyone, but according to Wort.lu yesterday (3 September 2012), Countess Stéphanie de Lannoy is to become a citizen of Luxembourg when she marries Hereditary Grand Duke Guillaume.
The bill was filed in the Chamber of Deputies yesterday and is expected to be voted on in early October.
Wort.lu claims that the act will come into force on 20 October 2012, the day the religious celebration takes place in the Notre Dame Cathedral in Luxembourg. However, I can't find anything in the bill that explicitly states when the act is to come into force. It would also make more sense - at least to me - if the act comes into force on the date of the couple's civil wedding on 19 October. I guess we will know for sure when the promulgated law is being published in the legal gazette (Mémorial).
The bill (no. 6474 (2011-2012) can be read here.
Updated on Wednesday 5 September 2012 at 08:10 (minor correction).