Valero will join Villarreal on a season-long loan move with a view to a permanent deal.
“After relegation in 2009 we agreed to loan Borja to Real Mallorca,” West Brom sporting and technical director Dan Ashworth told the club’s official website.
“On the back of an outstanding season in Spain, and taking into account his professional and personal wishes, we decided to accept an offer from Villarreal.
“I’d like to thank Borja for his contribution and his professional attitude throughout the last two years. And we wish him well over the coming season.”
