According to an affidavit sent by Mr Villarejo to the examining magistrate at Spain's National Court who is currently investigating 27 different criminal cases in which he is implicated, the former policeman said he was sent to London to gain Ms zu Sayn-Wittgenstein's confidence, in order to "neutralise" her as a threat to the stability of the Spanish monarchy.
In the document, seen by the BBC, Mr Villarejo claims that agents from Spain's CNI intelligence service "instructed me to gain Princess Corinna's trust in order to recover especially sensitive documents she held".
According to prosecutors whose investigation was unsealed last year, Mr Villarejo and other police officers, acting on orders from interior ministry officials, mounted an espionage operation to seek and destroy files that Bárcenas or his wife had in their possession, thus concealing evidence from the judicial probe into the PP's finances.
A popular period and fertility tracking app has settled with the Federal Trade Commission over allegations that it lied to users about sharing private health information with third-party firms, including Facebook and Google.
Then it shared their sensitive health data, including the dates of their periods and their pregnancy plans, with outside companies that provided marketing and analytics services to the app.
As some users are more willing to share private information with an app like Flo than a major social network, the disclosures can feel invasive.
News of the settlement follows a 2019 report from The Wall Street Journal, which revealed that Flo was secretly sharing sensitive user data with Facebook.
A 2019 study published in JAMA Network Open also showed that apps marketed to people with depression or who wanted to quit smoking were sharing health data with Facebook and Google as well.