The envelope is fairly typical for the Belgium Royals. This envelope features a purple crown with the words "Secrétariat de la Renie/Queen's Secretariat."
Inside is the Belgium Royal's usual birthday reply, a typed card and photo.
The card reads:
Royal Palace of Brussels
Accompanying the card is a photo of Princess Elisabeth taken this summer as part of a set to mark King Philippe's 5th Anniversary of Accession.
Their Majesties the King and the Queen express their sincere thanks for the good wishes you addressed to Princess Elizabeth on the occasion of her 17th birthday.