Right-back Fabinho will remain with Monaco next season after his loan from Portuguese club from Rio Ave was converted to a permanent deal.
Fabinho has played at Monaco since 2013 and signed a contract to tie him to the Principality club until 2019.
The 21-year-old made 35 appearances in Ligue 1 this season and signed despite reported interest from Barcelona.
Earlier this month, Fabinho received his first call up to the Brazil national team for this summer's Copa America.
The 21-year-old told the club's website: "I am very happy to sign a contract with AS Monaco, I have had two good seasons here.
"We were second in the league last year, we are third now and we hope to confirm third place and I hope to achieve good things with AS Monaco."
The club's vice-president Vadim Vasilyev added: "Fabinho has shown all his talent since his arrival and we are happy to sign him definitively.
"His versatility, his youth and his attitude mark him out as a player with a big future. It is also a source of pride to see him make it into the Brazilian squad."
Also on Tuesday, Monaco announced that 19-year-old defender Almamy Toure also signed a contract to keep him at the club for an additional four years.