There is a little-watched video on YouTube taken in a Belgian back garden in 2007. It shows the feet of a14-year-old footballer performing tricks and curling shots past a hapless goalkeeper.
The striker is Thibaut Courtois. The hapless keeper is his friend, Jens Brulmans.
"We wanted to film our best goal," said Brulmans. "When we played in the garden, Thibaut was just playing as an outfield player, because he was too good as a goalkeeper. We couldn't beat him."
Courtois is the goalkeeper Chelsea signed from Genk for pounds 7 million in 2011, three years after he had filmed himself scoring past Brulmans in the back garden for the final time. He is yet to make an appearance for Chelsea but is now being talked of as the best goalkeeper in the world. Tonight he stands in the way of Barcelona and Lionel Messi in the quarter-finals of the Champions League.
The 21-year-old is in his third season on loan at Atletico Madrid and is still expected to return to Stamford Bridge in the summer as Petr Cech's 10-year tenure in Chelsea's goal looks to be coming to an end, even though the Belgian's future is the subject of daily transfer rumours.
Courtois helped Atletico win the Europa League in 2012 and earned a reputation as one of the best emerging goalkeepers in world football in his first season in Spain. Then manager of Real Madrid, Jose Mourinho had a scouting dossier drawn up on him.
At the start of his second season on loan, Courtois was part of the Atletico team who beat Chelsea in the Super Cup. He finished the campaign with a Copa del Rey winners' medal, the Trofeo Zamora award for the goalkeeper who conceded the fewest La Liga goals and qualification for the Champions League. Now his Atletico side are fighting for Spain's La Liga title. A
2-1 win at Athletic Bilbao on Saturday keeps them a point ahead of Barcelona. Courtois made a typically agile save to preserve Atletico's lead and he has given his side the belief that they can knock Barcelona out of the Champions League.
Courtois has two years remaining on his Chelsea contract but is not prepared to return as an understudy to Cech. He says he will force the Blues to pick between the pair. After the Bilbao game, he said he would reveal his destination imminently. The football world awaits his decision with interest.
The rapid rise of Courtois is no surprise to those who have charted his career from long before he started making YouTube films.
Even though children in Belgium cannot play competitive football before the age of six, Courtois joined his local club, Bilzen VV, as a five-year-old and immediately impressed against his older team-mates. "He was a robust little kid," said Bart Theunissen, Courtois's first coach. "A quiet guy, but at that time already a no-nonsense person. We didn't have a real goalkeeper, we did a rotation, which is usual at that age, but you already saw he had some good reflexes."
Three years later, Genk took Courtois on trial before signing him and the youngster initially combined football with volleyball. During the summer, he played in tournaments with his elder sister Valerie, who is now an international Belgian volleyball player, and recreationally with father Thierry and former international Kristof Hoho.
"We teased each other a lot," said Hoho. "Once, I even threw Thibaut in the garbage bin, we had a lot of fun together."
Courtois played in various positions during his early years at Genk, until the goalkeeping coach of the club's youth teams, Gilbert Roex, suggested he should concentrate his efforts between the posts.
"He was a laid-back guy, relaxed, he learnt things easily, he had the right co-ordination of his body and those amazing reflexes," Roex said. "Until his 12th birthday, he was regularly playing outfield. His parents didn't want us to pin him down on one position."
Rising through the ranks at Genk, Courtois was regularly fighting for a goalkeeping place with Koen Casteels, who now plays in the Bundesliga for Hoffenheim. They are the same age and showed similar potential, but Casteels was physically more mature.
"When he was 13 or 14, there were some doubts he would ever make it," Roex said. "He grew a lot in a short time and he really looked clumsy. Some coaches raised their doubts and at a certain point the youth directors were even thinking about letting him go. But we, as goalkeeper coaches, saw he had something special."
Gitte Lambrechts, Courtois's mother, said: "At that time, I was even thinking Thibaut was just not hard enough for football. When he wasn't selected for the national team, he was very disappointed. But his dad and my father have always encouraged him to work hard and never let his head drop."
Brulmans, a nephew of tennis star Kim Clijsters, was the more talked-about kid in the neighbourhood, but a year after he and Courtois filmed their final YouTube video in April 2008 Courtois received his big break at Genk when interim coach Pierre Denier was hit by a goalkeeping crisis that included an injury to Casteels.
Aged 16 years and 341 days, Courtois was handed his debut against AA Gent and from that moment became an integral part of Genk's first-team squad. Having rejected the opportunity to move to Hoffenheim in 2010, Courtois grasped his next big chance when Genk's Hungarian No?1, Laszlo Koteles, had registration problems and was not eligible for the first game of the 2010-11 season.
Courtois made 40 league appearances as Genk became Belgian champions, conceding just 32 goals and keeping 14 clean sheets. On her son's incredible first full season, Gitte said: "Thibaut sometimes still played football with the kids in the neighbourhood on Sundays. He taught them tricks and gave his gloves to a young boy who wanted to become a goalkeeper.
"He told me that he still thought about how he was as a boy, how happy he felt he could be on a picture with one of Genk's goalkeepers. That's why he will never say no to a kid begging for an autograph."
Chelsea would love Courtois to put his autograph on a new five-year contract, but he will demand he is allowed to keep growing - at Stamford Bridge or elsewhere.