Theo Walcott came through the youth ranks at Southampton before joining Arsenal in a big-money move in January 2005. Arsenal raided the Saints again last summer when securing Alex Oxlade-Chamberlain in a £12m deal.
Walcott told the club's website: "It will be a very tough occasion against Southampton, but it is one I am really looking forward to.
"It will be a very special moment for me and Alex, and also for some of the fans to see us come back to the club."
"They have done a fabulous job - you also look at Gareth Bale and what he is doing now at Tottenham," he said.
"It is down to the quality of their scouting, the quality of their coaching and education."