They won a World Cup together. They dominated English football together. They were Invincible together.
But now, both in the infancy of their managerial careers, Thierry Henry and Patrick Vieira are rivals.
They remain close, both as friends and geographically – the Stade Louis II, where Henry manages Monaco, and the Allianz Riviera of Vieira's Nice are only a half-hour's drive apart.
Their respective clubs share only antipathy, however. And, both desperate for points, Wednesday's Ligue 1 showdown in the Principality will see the two budding French tacticians put their friendship to one side in search of victory.
The first managerial meeting between the Arsenal and France legends was initially supposed to take place in December, only for the fixture to rearranged after the police advised protests in France at the time rendered it unsafe. But the plights of the two sides and the identity of their managers ensure the game has lost none of its intrigue.
When Henry replaced Leonardo Jardim on October 11, he found Monaco in 17th place, without a victory since the season's opening weekend. It seemed the only way was up for the 2016/17 champions, whose squad possesses enough individual talent to be much higher, but the Monegasques must now confront the very real prospect that they could go down.
Henry's arrival in his first managerial position, having previously been assistant to Roberto Martínez with the Belgium national team, was accompanied by no “new-manager bounce”: he has overseen only two Ligue 1 wins in his nine games in charge, with Monaco now 19th in the 20-team division and five points adrift of safety.
Things aren't so bleak for Vieira. Having started his coaching career with Manchester City, taking charge of the Premier League champions' Elite Development Squad, the former Juventus and Inter Milan midfielder enjoyed a successful spell at New York City FC – improving their standing in each of his full seasons at the helm – before taking over at Nice last summer.
Les Aiglons currently find themselves tenth in Ligue 1, having finished eighth last season. Such is the logjam in the upper-middle part of the French top flight, however, that a win over Henry's Monaco could see Vieira's side climb as high as sixth.
With a greater breadth of experience, Vieira is viewed as the better tactician of the pair, operating with a 3-5-2 system which prizes solidity – Nice have conceded just 17 goals in 18 games this term – while offering freedom to gifted attacker Allan Saint-Maximin and midfielder Wylen Cyprian, the team's joint-top scorers.
On paper, Monaco have the more talent-rich squad, yet Nice are a much more cohesive unit, even if they do lack goals – they average only 0.72 goals per game this season.
By contrast, Monaco leak like a sieve, shipping 29 in their 18 league fixtures, and there is a growing feeling that Henry is unable to get his message across to his players.
The legendary striker would refute that claim, though. After a come-from-behind cup victory over Rennes in midweek, the former Barcelona striker praised his side's fighting spirit and how work on the training field was beginning to bear fruit.
“What particularly pleased me tonight is the attitude of the players who have always tried to improve,” Henry said, after Monaco prevailed on penalties.
“We conceded a goal and we reacted. I liked it, and it's very important. The fans saw a team who fought.
“It is always a satisfaction as a coach to see on the pitch what we have been working on in training. We will not give up. There has been work done, and work that remains to be done.”
With Henry battling relegation and Vieira treading a thin line between mid-table mediocrity and what would be a CV-boosting push for European qualification, there is a lot a stake for the two nascent managers in Wednesday's Derby de la Côte d'Azure.
No matter the result, it seems the pair – who roomed together on away trips while at Arsenal – back each other to succeed as coaches, each recognising in the other the traits of personality necessary for managerial success.
“There is a friendship between Pat and I. Pat is a reference not only for me but for everyone,” Henry said ahead of the rearranged Monaco-Nice meeting in December. “He's always been a prodigy, the first in the class, someone who always keeps going. He's a great guy.”
And Vieira lavished praise on Henry in his autobiography, long before Arsenal's all-time leading scorer turned his hand to coaching.
“One of Thierry's great qualities is that he is a really hard worker,” Vieira wrote. “He often stays behind after training to put in extra sessions, he is never satisfied and constantly believes he can progress … above all, he has a passion for football.”
However, after spending six years together at Highbury, the key figures in two Premier League title triumphs and two FA Cup wins, architects of a historic unbeaten season, Henry and Vieira must put friendship and mutual admiration to one side when standing in opposing dugouts on Wednesday night. For 90 minutes at least.