According to one of the many conversations with the rich and powerful that Villarejo recorded as a private investigator, zu Sayn-Wittgenstein said that a French doctor who had treated Jacques Chirac had analysed Juan Carlos and concluded that he had been given "a lot of female hormones to take away his strength".
Apart from zu Sayn-Wittgenstein, Juan Carlos is rumoured to have had many lovers during his nearly four decades on the throne, including a Miss World contestant called Bárbara Rey, who allegedly received millions of euros from state coffers to maintain her silence on the affair.
Juan Carlos apologised to Spaniards in 2011, when it was revealed that he had been on a secret elephant hunt in Botswana in the company of zu Sayn-Wittgenstein during a deep financial crisis in Spain.
Villarejo faces possible criminal charges in more than 20 further investigations into his spying activities. While he was in preventive custody between 2017 and March of this year, some of his tapes were leaked to the media, including one in which zu Sayn-Wittgenstein can be heard describing alleged attempts to launder money earned through kickbacks by Juan Carlos.
That tape led to an ongoing investigation in Switzerland into several of Juan Carlos' associates and offshore funds, which are also being probed by prosecutors at Spain's Supreme Court.
Villajero's comments on Wednesday came at a commission set up to investigate the use of classified security funds and secret police agents by the Spanish government under former Prime Minister Mariano Rajoy.
