According to a new book called “Final De Partida” ("End Game"), Juan Carlos, the former king of Spain, was leading a double life and having an affair with a German aristocrat for the last 10 years of his reign.

The juicy allegation is that Juan Carlos was secretly seeing a woman named Corinna zu Sayn-Wittgenstein and was in fact so taken with her that he even contemplated divorcing from his wife, Sofia.

The book was written by Ana Romer, a former royal correspondent for the El Mundo daily, and it sold out its first printing of 25,000 copies within 24 hours.

As quoted in The Daily Mail, Romero said, during a book launch in Madrid, that what one would find in her book was the description of a “double life which Juan Carlos led during a long time, a double life which obviously has not gone well.”

Romero bases her shocking claims upon 100 interviews with anonymous sources. According to the author, the affair ended in 2014 when Juan Carlos was abdicated from the throne in favor of his son, Felipe.

Juan Carlos married former Queen Sofia in 1962 and became king in 1975.

Romero stated that her book “is a chronicle of the end of an era, when Spaniards turned their backs on Juan Carlos.”

Publishers have already ordered a second print of the gossipy account.

Sayn-Wittgenstein was born a Danish national in 1964 in Frankfurt, Germany. The 50-year-old woman has been married twice, once in 1989 to an English businessman named Philip Adkins and again in 2000 to Prince Casimir zu Sayn-Wittgenstein-Sayn.

As reported in a Vanity Fair article, when it was revealed in 2012 that Sayn-Wittgenstein had accompanied Juan Carlos on a hunting trip, much scandal ensued and the socialite went on to deny any “improper relationship” with the King.