The Hornets swooped for the former West Ham whizkid on Premier League deadline day.
And AS says it was Quina's older brother, Samuel, who was key to Watford winning the race for the Portuguese youngster's signature.
Real and Barca had also made offers to Quina this summer after it became clear that he would be leaving West Ham.
However, it was Samuel who convinced his brother to remain in England and sign with Watford. Samuel isn't an agent or adviser, but was the biggest influence on the decision to move to Watford last week.
It's suggested Samuel believes Watford present Quina's best chance of first team progress.