The Gunners youngster is back in north London after a successful loan spell with 1899 Hoffenheim.
Nelson scored eight goals and made five Champions League appearances with the German side.
And this has earned five appearances for the England under-21s, where he has scored two goals.
Footage has now emerged of the pair enjoying a game together.
In the clip, Sancho is playing “Roomates” with the Arsenal star.
The 19-year-old has to guess the right answers to question about his team-mate, who cannot hear the question, and wins if the answer matches.
Dortmund’s star forward is asked what instrument Nelson plays.
Nelson’s error comes as:
“Great spelling there”
He has the options of drums, keyboard and guitar to choose from.
“It’s guitar – I know that one,” Sancho quickly replies.
The Arsenal youngster has to write down the correct answer – and it is right.
He adds: “I’m still leaning.”
But Nelson’s card shows a major error, with “guitar” having an “e” for the “a”.
This footage was shared on the Three Lions’ official YouTube channel, where it has been viewed more than 250,000 times.
And the Gunners faithful were in stitches at their youngster’s gaffe.
“Nelson spelling guitar wrong, fantastic stuff,” one supporter said.
Another commented: “Love that.”
While a third simply said: “Great spelling there.”
This comes as Gunners’ five most likely summer signings have been predicted by a supercomputer.
You can read Arsenal’s full list of Premier League 2019/20 fixtures here.