The Belgium Royals have a number of different envelopes that they use. This version is the most common for King Albert & Queen Paola, with a purple crown and Belvédère [Castle], the name of their home, on the front.
What is unusual however is my address is handwritten on the envelope. I have gotten a number of replies over the years with handwritten envelopes, but this is the first time from Belgium.
Inside is a flat card, similar to past birthday replies.
The card says:
His Majesty King Albert II warmly thanks you for the kind wishes sent on the occasion of His 86th birthday.