Walcott went on to make almost 400 appearances for Arsenal and scored over 100 goals for the Gunners in all competitions.
Now aged 31, Walcott joined Everton in 2018 for £20million but the England international, who has 47 caps to his name, has fallen down the pecking order at the Toffees since manager Carlo Ancelotti joined the club.
After 14 years away, Walcott said it will be emotional to play for Southampton once again.
“I had a few opportunities from other clubs, but as soon as Southampton came in for me, it’s part of me and has made me into the player I am. It’s in my heart,” Walcott said. [H/T BBC Sport]
“I will probably cry, I bet, when I first play, and it means so much. All the people that made it happen, I can’t thank them enough. Honestly, I’m so pleased.
“I was seriously lost for words when Southampton came on the table, and for me it was such an easy decision.
“To get the chance to work with the manager as well and these young players that are coming through, I feel like I’ve made the right choice.”
Southampton announced the Walcott deal with just minutes to spare of the transfer window closes, though a domestic-only window for trades between Premier League and EFL clubs doesn’t end until 16 October.
In other Saints news, a variety of Southampton players left the club today.
Wesley Hoedt joined Lazio on loan, while Sofiane Boufal returned to France to join Angers on a temporary deal.
Meanwhile, former record signing Guido Carrillo terminated his contract at Southampton to join up with Elche on a free.
When does the summer transfer window open and close?
The summer transfer window opened on 27 July and closes at 23:00 on 5 October.
A domestic-only window for trades between Premier League and EFL clubs will run from 5 October until 16 October at 17:00.