A man who claims he was molested by George Pell in a swimming pool in the 1970s is filing a lawsuit against the cardinal.

The man, who was one of four complainants to give evidence against Pell in the now-dismissed second trial, alleges that the cardinal and a nun assaulted him while he was resident in St Joseph’s boy’s home from 1974 to 1978.

The lawsuit, filed at Victoria’s supreme court, also names the Sisters of Nazareth (who were responsible for the management of St Joseph’s at the time), the state of Victoria and the Archdiocese of Melbourne.