Pompey have brought Ryan Williams back to Fratton Park.
Kenny Jackett has swooped for the out-of-contract winger, who started his career with the Blues.
The Australian made 41 appearances for Championship side Rotherham last season.
However, he has elected to return to the south coast – and the club he left seven-and-a-half years ago.
Williams has signed a two-year deal and represents Pompey’s fourth signing of the summer.
The tricky wideman emerged through the Blues’ Academy to make six appearances during the 2011-12 campaign, when managed by both Steve Cotterill and Michael Appleton.
Then, in January 2012, he was sold to Fulham for an undisclosed fee following a successful trial match.
The 25-year-old has gone on to represent Oxford United, Barnsley and Rotherham.
Earlier this month, Williams made his Australian international debut, appearing as a second-half substitute in a friendly against South Korea.
He joins James Bolton, Ellis Harrison and Paul Downing as close-season recruits by Jackett.