In his 500-page book, the 87-year-old former monarch reviews well-known moments from Spain's history as well as his extramarital affairs and financial scandals.

Among its most controversial passages are Juan Carlos's warm words for Spain's late dictator General Francisco Franco and reflections on his role in the country's transition to democracy.

Sanchez told daily El Pais that while he had not yet read the memoirs, based on the excerpts he has seen "it will not be one of the books I recommend for this Christmas."

"I will respond to some of the points that surprised me, about who did or didn't bring democracy. Democracy didn't just fall from the sky; it was the result of the struggle of the Spanish people, of everyday citizens," the Socialist premier added.

The memoir, "Reconciliation", was published in French on Wednesday and is set for a Spanish release on December 3.

"I gave freedom to the Spanish people by establishing democracy," Juan Carlos asserts in the book.

Franco separated Juan Carlos from his parents when he was 10 and groomed the boy to be his successor.

He was crowned two days after Franco's death in 1975.