In his 500-page book, the 87-year-old former monarch reflects on 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 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.

Juan Carlos disappointed Francoists who hoped he would continue the dictator's legacy by quickly implementing reforms that led to democratic elections in 1977.

He abdicated in favour of his son, Prince Felipe, in 2014, and has lived in self-imposed exile in the United Arab Emirates since 2020.

Sanchez praised Spain's King Felipe VI in the El Pais interview, saying he was carrying out his duties "commendably".

Juan Carlos' memoirs have sparked criticism from other politicians.

Spain's Culture Minister Ernest Urtasun condemned the former monarch's praise for Franco on Thursday, calling it "sickening that nowadays someone would still dare to defend or justify the dictator".

Former Socialist Prime Minister Jose Luis Rodriguez Zapatero said Juan Carlos should have "tempered his words" about Franco, whose regime relied on executions and imprisonments of political opponents.

Juan Carlos wrote in the book that he decided to publish his memoirs because his story "was being stolen from me".