Everton make move for Mustafi
"This is an important step in my career," he said. "I was a bit down when making the decision."
While Hamburg - managed by former Tottenham boss Martin Jol - are less than impressed at having watched one of their stars of the future walk away from the Nordbank Arena at such an early age.
"We really tried to keep Shkodran at our club, but when there is a club from England coming up we are unable and unwilling to compete financially," Jens Todt, head of Hamburg's youth academy, told Hamburger Abendblatt.
"It's it tough to accept, but it will not destroy us. We are just hoping this is not going to happen too often again."