Real Madrid have presented Brazil's 18-year-old Vinicius Junior as their new £38.7m signing at the Bernabeu Stadium.
The teenager, who can play as a winger or forward, joins from Flamengo after a deal - which is a record for a player under 19 - was agreed a year ago.
Madrid president Florentino Perez said: "He's a player who is already considered one of the great hopes of Brazilian and world football."
Vinicius made 37 league appearances for Flamengo, scoring seven goals.
He played a significant part in the club's rise to the top of Brazil's Serie A, contributing six goals and three assists in their opening 11 league and Copa Libertadores matches.
Voted the best player when Brazil won the Under-17 South American Championship last year, Vinicius originally agreed to join Madrid after playing only 17 minutes of senior football.
Presented on the pitch alongside his compatriot, Ronaldo, who scored 104 goals in 177 games for Real between 2002 and 2007, he said: "This is the best opportunity a football player could have.
"I'm honoured to have reached the pinnacle in football, Real Madrid, at only 18 years of age."
The fee surpasses the initial £36m paid by Manchester United to Monaco for striker Anthony Martial, who was 19 when he became the world's most expensive teenager in a September 2015 deal that could be worth up to £58m.
However, it is well short of the £166m fee that Paris St-Germain have agreed to pay Monaco for 19-year-old French World Cup winner Kylian Mbappe, who was on loan with them last season.