The teenager has signed a three-year deal with the reigning Ligue 1 champions leaving Osasuna, where he made his professional debut last year
Monaco have signed Osasuna goalkeeper Alvaro Fernandez to provide competition for Danijel Subasic and Diego Benaglio.
Fernandez, 19, has signed a three-year deal with the Ligue 1 champions.
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The Spain youth international made his LaLiga bow last season as a half-time substitute in Osasuna's 3-1 defeat at Villarreal and the teenager kept a clean sheet in the second half.
"I am very happy to sign at AS Monaco, a club that has demonstrated all its sporting ambition last season and which relies on young players," Fernandez told the club's official website.