The son of Beppe Grillo, comedian and co-founder of Italy’s Five Star Movement, is under investigation by police and prosecutors after being accused of gang rape with three of his friends.

Ciro Grillo, 19, is facing allegations that he and the other men raped a Scandinavian model at the comedian’s villa at Porto Cervo on Sardinia’s exclusive Costa Smeralda during their summer vacation.

Five Star is a partner in Italy's new governing coalition, which took office on Thursday. The rape inquiry coincides with the re-emergence of Beppe Grillo who urged the party leader, Luigi Di Maio, to join the centre-left Democratic Party and avoid snap elections.

According to Italian media, Ciro Grillo and the three others met the woman, who has not been named, at a nightclub in Porto Cervo and after a night of heavy drinking they returned to the Grillo family’s luxury villa where the alleged rape took place on July 16.

Lawyers for Grillo and the other accused say the defendants have not denied having sex with the 19-year-old woman but claim the sex was consensual.

The four accused, who come from the northern city of Genoa, were interrogated for several hours on Thursday by public prosecutor Gregorio Capasso in the Sardinian town of Tempio Pausania.