Tavares made his debut for the U21s in victory over Chelsea last week.
"My agent called me to say he'd spoken with the coach, with Martin Jol, who I worked with in Hamburg," he told fulhamfc.com when asked as to how the move came about.
"I am looking forward to working with Martin Jol again. He brought me to SV Hamburger but he didn't stay for long as he moved to Ajax, so I'm very happy to see him again and I want to thank him for giving me the chance to play in the Premier League and show everybody what I can do.
"I think it's the dream for everybody to play in the Premier League. I was at Middlesbrough in the Championship and that was a good experience but the Premier League is something else so I'm very happy to be here."