Former Spanish Prime Minister Jose Luis Rodriguez Zapatero, an ally of current Socialist Premier Pedro Sanchez, is being investigated for alleged influence peddling and related crimes, the country's top criminal court said on Tuesday.

Zapatero has thus become the first Spanish prime minister — current or former — to be formally investigated by the judiciary since Spain's return to democracy following the death of longtime dictator Francisco Franco in 1975.

The announcement comes as Sanchez himself is under pressure amid an investigation into alleged kickbacks involving key members of his ​inner ‌circle, as well as probes focusing on his wife and his brother.Why is Zapatero being investigated?

The investigation is part of so-called Plus Ultra case, which centers around the state bailout of the domestic airline Plus Ultra through the state holding company SEPI during the coronavirus pandemic.

The €53 million ($62 million) bailout, which came in 2021 and thus years after Zapatero had left office in 2011, was sourced from COVID-19 recovery funds.