Unknown - Help to identify

[aidab]

I would appreciate any help to identify this coin. It shows a human bust facing right in one side. In he other side, I think I can read the word REX at the bottom ?
It weights 7,2 GR. and it's diammeter is about 22 mm.

[Dapsul]

I would start the search in Spain, but this is just an idea.

Frank