I know someone already answered you but http://www.thefa.com/football-rules-governance/policies/player-registration/international-clearance
I didn't know the answer either, good info there.
Delighted. He's too good for us, expected to see him at Milan or Roma for example next year, not the Albion. I am very, very excited.
Oh and if you wonder about his ability to make it in the EPL, ask ex champions Leicester. My LCFC supporting mates reaction to him maybe lining up against them...