He was arrested in relation to the Regency Hotel shooting in Dublin in 2016.
The 58-year-old was detained in Fuengirola yesterday afternoon, after a European Arrest Warrant was issued in April.
He's wanted in connection with the murder of Kinahan gang member, David Byrne, in the Regency over five years ago.
He'll now appear before a court in Madrid - and Irish Independent journalist Paul Williams says he can do one of two things.
