All indications are that it started when Kevin De Bruyne fell asleep on the Chelsea team bus on the way to an away game.
He didn’t often need to have the adrenalin pumping back then, of course, because there was very little chance of him actually playing.
De Bruyne’s teammate and fellow countryman Romelu Lukaku was in the same boat too, and when he filmed the midfielder dozing off he immediately put it out on social media.
“You are caught sleeping, boy” was his giggly take on it all, to which De Bruyne could only laugh.
The two of them had to laugh back then because the alternative would have got them down.
It was Lukaku who had arrived first.
The incredibly gifted teenager had been the talk of the football world after making his Anderlecht debut two weeks after turning 16 in May 2009.
He would go on to score 41 goals in 98 appearances over the next two years, and seemingly had his pick of clubs when he joined Chelsea for a fee rising to £17million in August 2011.
He was still only 18, but his prolonged exposure to first-team football at Anderlecht had turned him into a young man in a hurry, and so only getting 12 appearances – and scoring no goals – in his debut season wasn’t enough, he wanted and needed more.
Halfway through that debut season Chelsea had announced the £7million signing of the 21-year-old midfielder De Bruyne from Genk, although he was to spend the remainder of the 2011-12 campaign at his first professional club.
After finally linking up with his new employers ahead of the following campaign he didn’t do enough to convince Roberto Di Matteo that he could break into the European champions’ side, and so was shipped off to Werder Bremen on loan.
The same could be said for Lukaku, who didn’t make the bench for that Munich final, and he was off to his own WB, West Brom.
The pair stayed in touch though, and remained close friends.
They had both already made their senior international debuts for Belgium by this point, doing so back in 2010, and there was something about being frozen out at Chelsea that seemed to fuse them together and create a kinship that they would take onto the field.
By the end of their respective loan moves they’d have hoped to demonstrate this connection back at Chelsea, where Jose Mourinho was in situ again following the brief, Europa League-winning spell of Rafa Benitez.
The prospects looked good for both Belgian youngsters when they started the 2013-14 season as members of Mourinho’s squad, with Lukaku coming off the bench in a couple of Premier League games and De Bruyne memorably starting at Old Trafford when Chelsea played without a striker (Lukaku was an unused sub).
Soon they were off again though, with Lukaku going to Everton on loan for the season and then De Bruyne leaving for Wolfsburg in an £18million permanent deal in the January.
The two would never be on the same club side again, but the friendship has remained.
Seven-and-a-half years later De Bruyne and Lukaku are leading their nation’s charge at the European Championships, a tournament that many fancy Belgium to win and largely because of these two.
League titles, player of the year awards, money-spinning transfers and enormous contracts have featured heavily in their careers, as well as a fair share of criticism from fans and pundits too.
But they’ve always had each other.
“With Kevin, I have the best friendship in the entire national squad,” said Lukaku in Simon Mullock’s Sunday Mirror exclusive last weekend.
“We tell each other stuff that we don’t tell other people. We trust each other massively.”
Their special handshake goal celebration might not be one of football’s most famous acknowledgements of a goal – usually one scored by Lukaku that De Bruyne has assisted – but is something that is deep and personal to them.
“You see this kind of celebration in the NBA,” De Bruyne has said.
“But, in all honesty, their handshakes are 10 times more complicated to do.
“This has become our handshake after a goal, although I don’t want to make it too much of a big thing.”
That attitude sums up their rather low-key approach, with the pair’s relaxed nature and ability to stay calm in the most pressurised football situations also key to their friendship.
There is another reason why football should celebrate their bromance though, especially in these times.
“I love that picture of the two of us. It is everything,” said De Bruyne when looking at the recent photo of the pair celebrating against Finland.
“The atmosphere, the combination of black and white players. It shows diversity.
“That’s what makes the photo beautiful.”
It makes the friendship pretty nice too.