The Basics:
We have a lot of helpful general information on writing to the Royals under our "How to" tab. This post will just cover some specifics about writing for today's announcement.
The Address:
Palais Grand-Ducal
B.P. 331
L-2013 LUXEMBOURG
There are a lot of ways you can refer to the couple, including:
- TRH Prince Guillaume & Princess Stéphanie
- Hereditary Grand Duke Guillaume & Hereditary Grand Duchess Stéphanie
- The Hereditary Grand Duke & Hereditary Grand Duchess
- etc.
What you use is a matter of personal preference and how formal you want to be.
When to write?
You don't need to worry about getting your letter/card out the same day as the announcement. I think a good rule is to try to send out your congratulations within 2 weeks of the announcement.
Will they reply?
Yes, I would expect so. The Luxembourg Royals usually reply with a flat card printed for the occasion. I expect it will be similar to Prince Felix and Princess Claire's pregnancy or birth reply for Prince Liam.
And I would expect a longer response time than usual given that the Palace will have to deal with Pregnancy and Christmas mail all at once, and both are big occasions to write to the royals.
