The 19-year-old midfielder has been released by the Blues – and the Isthmian League premier division side have been quick to snap him up.
A Rocks tweet on Friday night said: ‘Welcome, Josh Flint! The young midfield prospect has signed for the Rocks after being released by Pompey today.
‘Josh is a familiar figure at the club, having already played for us this season on loan - he goes into the squad for the Isthmian League home game versus Folkestone.’
Flint, from Waterlooville, had been with Pompey since he was 11.
The former Fratton Park season-ticket holder scored and helped himself to an assist in September’s 3-1 Leasing.com Trophy victory over Norwich under-21s.
It represented his Blues debut, having emerged through the academy set-up alongside Bradley Lethbridge, Joe Hancott and Leon Maloney.
Flint later started the final EFL Trophy group match at Oxford United, although was substituted at half-time for Gareth Evans in the 2-2 draw.
Another young player released by Pompey, defender Joe Dandy, has also been playing for the Rocks.
Meanwhile, Dan Smith, who left the Blues last year, is Bognor's top scorer.
In addition the Rocks currently have defenders Harry Kavanagh and Matt Casey plus striker Brad Lethbridge on various loans from Fratton Park.