The two envelopes are identical from the front.
However, what is interesting is the two envelopes are different brands.
Christmas
The top of the letter features King Juan Carlos' coat of arms in purple with "Household of H.M. The King. The Head Secretariat of H.M. King Juan Carlos" written underneath. Last year's Christmas reply had this in more of a blue color. I'm not sure this was a conscious color change or just something with the ink.
The letter is in Spanish and translates to:
Palace of Zarzuela (The couple's official residence)
January 30th, 2018
Ms. Gertrude Alexandra Daly
(My Address)
The Head Secretariat of H.M. King Juan Carlos
Their Majesties King Juan Carlos and Queen Sofia, have received with great pleasure the best wishes that you have sent them for Christmas and New Years and they have asked me to convey their most sincere gratitude to you, as well as their best wishes for you this new year.
I take this opportunity to send a cordial greeting,
Alfonso Sanz Portolés
I'm still waiting on a few more Christmas replies, mainly from the UK (Queen & Philip, The Cambridges, and Harry).
Juan Carlos' Birthday
The 2nd letter for is King Juan Carlos' 80th Birthday.
The letter is in Spanish and translates to:
Palace of Zarzuela (The couple's official residence)
February 5th, 2018
Ms. Gertrude Alexandra Daly
(My Address)
The Head Secretariat of H.M. King Juan Carlos
His Majesty The King has asked me, in his name, to send his sincere thanks, together with his affectionate greetings, for the warm wishes that, on the occasion of his Birthday, you have been kind enough to send.
Upon fulfilling this request, I send a cordial greeting,
Alfonso Sanz Portolés