Hornets chairman Graham Simpson told the club's official website: "As a club we're very happy with the news.
"We always knew we had a strong case and, despite our setbacks, we knew we had to fight for what we believed to be right for this young man.
"Al will now continue to contribute to our society, which I know he feels a debt of gratitude towards.
"I'd like to personally thank all the Watford fans whose backing of Al has been so crucial to moving this forward and securing his immediate future in the United Kingdom."