For the 20-year-old, it represents the next step in what promises to be a strong career, as he looks to break into the Premier League.
But he’s not the first figure to swap ends of the M27 in recent years.
So who will he join by doing so?
Here’s the names to have played at Fratton Park and/or The Dell/St Mary’s since the turn of the millennium, after representing one side of the south coast derby.
. Collage Maker-10-Jun-2022-12.19-PM.jpg
David Connolly, Peter Crouch, Gavin Bazunu, Nigel Quashie Photo: The News
. Dave Beasant
Pompey appearances: 28 (2001 & 2002) , Southampton appearances: 108 (1994-97). Picture: Steve Reid Photo: Steve Reid
. Martin Cranie
Pompey appearances: 5 (2007-2009) , Southampton appearances: 25 (2004-2007). Picture: Joe Pepler Photo: Joe Pepler
. Eyal Berkovic
Pompey appearances: 28 (2004- 2005) , Southampton appearances: 34 (1996-97). Picture: Simon Bellis Photo: Simon Bellis
1. Dave Beasant
Pompey appearances: 28 (2001 & 2002) , Southampton appearances: 108 (1994-97). Picture: Steve Reid Photo: Steve Reid
2. Martin Cranie
Pompey appearances: 5 (2007-2009) , Southampton appearances: 25 (2004-2007). Picture: Joe Pepler Photo: Joe Pepler
3. Eyal Berkovic
Pompey appearances: 28 (2004- 2005) , Southampton appearances: 34 (1996-97). Picture: Simon Bellis Photo: Simon Bellis
4. Peter Crouch
Pompey appearances: 87 (2001-2002 & 2008-2009) , Southampton appearances: 33 (2004-2005). Picture: Clive Rose/Getty Images Photo: Clive Rose