Watford left-back Miguel Layun has finalised a move to Porto.
The Mexico international spent last season on loan with the Portuguese club, for whom he made 27 league appearances.
Layun's performances were good enough to convince the Porto hierarchy to turn the switch into a permanent one for a fee believed to be around £4m.
It is thought that Watford have negotiated a 20% sell-on clause as part of the deal.