Born in Stuttgart, Musiala spent a significant part of his childhood in England and was with Chelsea from 2011 until 2019, while he also captained the Three Lions at youth level.
However, he returned to Germany in 2019 to join Bayern Munich and elected to represent Die Mannschaft last year.
Musiala will now face off against the side he could have represented on Monday and made it clear he has no regrets about the decision on his international allegiance.
"I feel good to be here in England. I am very motivated. England are a very strong team and my past makes me want to play even more," he said.
"I don't know exactly how many times I've played at Wembley. I've been to school tournaments here before and made it to a final there twice. The atmosphere at Wembley is always great.
"It wasn't an easy decision and I thought about it for a long time. In the end it was a decision I made with my family and I'm very happy with. Some England fans are definitely not happy with my decision but that shows that I play well."
Flick has confirmed Musiala will start for Germany in its UEFA Nations League dead rubber at Wembley and heaped praise upon the 19-year-old.
"When he trained for the first time, you immediately noticed what a talent he is. His development is fantastic," he declared.
"He can hold his own well in a small space and has a strong feeling for the space. He is also very strong at dribbling, which is why he can solve situations for us.
"In addition, he is very skilled defensively and has many ball wins. I'm glad he's playing for Germany."