Goalkeeper Tom Heaton won three caps for the Three Lions during the prime of his career, making his debut as a late substitute in a friendly victory over Australia in 2016.
The 38-year-old was subsequently an unused substitute throughout Euro 2016 under Roy Hodgson, before also featuring in friendly contests with Spain and France in the early stages of Southgate's reign.
However, Heaton has not played for the Three Lions since that 3-2 loss to Les Bleus in June 2017, being ruled out of the 2018 World Cup with a calf injury and earning his most recent call-up in September 2019.
The ex-Burnley man is now third-choice at Manchester United behind Andre Onana and Altay Bayindir, failing to make a single appearance last season, and his contract expires at the end of the month, although he is said to be open to an extension.
Nevertheless, Heaton is now confirmed to be joining up with Jordan Pickford, Aaron Ramsdale and Dean Henderson and the rest of England's Euro 2024 squad in Germany, acting as a training partner for the goalkeeping trio.
Southgate "grateful" to Man United as Heaton joins Euros squad
England boss Southgate believes that Heaton will play an "invaluable" role in helping his fellow shot-stoppers, telling englandfootball.com: "I am really pleased Tom has agreed to join us in Germany.
"Experience tells us that a tournament can put a lot of demand on our goalkeeping group led by Martyn Margetson. Tom will play an invaluable role on the training pitch supporting Jordan, Aaron and Dean.
"Off the field as someone we all know well, he will add to the positive environment we are always looking to create. We are grateful to Manchester United for their support in making this happen."
The Man United veteran also reacted to the news on X - formerly known as Twitter - adding: "Incredibly honoured to be asked by Gareth to join the squad.
"To get the call to go to a major tournament, to help in anyway I can and pass on my experience is a proud moment. We have a great squad, I'm excited and can't wait to join the group."
England open their Euro 2024 campaign in Group C against Serbia on Sunday evening at the Veltins-Arena, prior to which Germany and Scotland get the tournament underway on Friday night.