For more new books about royalty see:

AUSTRIA
Author: Martina Winkelhofer.
Title: Sisis Welt. Der Alltag von Kaiserin Elisabeth zwischen Hof und Leidenschaften (Sisi’s world. The daily life of Empress Elisabeth between court and passions).
Publication: 6 April 2021 by Piper Taschenbuch (the publication has been postponed already several times, so hopefully not this time).
Language: German.

THE NETHERLANDS
Author: Rick Evers.
Title: Máxima, Meer dan Majesteit (Máxima, more than majesty).
Publication: April 2021 by Nieuw Amsterdam.
Language: Dutch.

THE NETHERLANDS
Author: Marcia Luyten.
Title: Máxima Zorreguieta. Moederland (Máxima Zorreguieta. Motherland).
Publication: April 2021 by De Bezige Bij.
Language: Dutch.