Bradley Lowery was picked last month to be a mascot for the World Cup qualifier against Lithuania, since when his hero Defoe has been brought back into the England squad.
The Sunderland fan, who has neuroblastoma, has struck up a friendship with the striker, with Defoe and other Black Cats stars visiting him in hospital when he was undergoing life-prolonging treatment.
His mother Gemma, from Blackhall, County Durham, told the BBC that Bradley was already excited to be asked to be a mascot for England - a role he has performed several times for Sunderland this season.
Speaking to Adrian Chiles on Radio 5 Live, she said: "To find out Jermain is going to be there as well just totally topped it off for him."
When Bradley was first invited, Mrs Lowery had warned Bradley that Defoe would not be in the England squad, so he would have to walk on to the pitch with another player.
"All of a sudden, we get told that Jermain has been called up," she told the radio show.
"For him to just be in the dressing room when Bradley goes is going to be absolutely fantastic for him."
Mrs Lowery said Bradley has got used to his relationship with the Sunderland star.
Read the full article on eurosport.co.uk: Brave mascot Bradley Lowery to lead England out with 'best friend' Jermain Defoe