Lewis Hamilton has just sealed his third Formula One drivers' championship, and Mercedes are celebrating their second successive constructors' crown, but all is not well inside the German team.
The relationship between Hamilton and team-mate Nico Rosberg—fractious since the early part of the 2014 season—appears to have reached a new low. First-corner incidents in Japan and the United States were followed by the now infamous cap-throwing episode before the Austin podium.
One week later, after an "angry" Rosberg had won the Mexican Grand Prix, Hamilton dropped a sly dig into the post-race press conference about the "gust of wind" that his team-mate blamed for his late, race-losing error in the U.S.
Writing in his Bild newspaper column, Rosberg later responded (h/t Autoweek) that Hamilton was "having a certain difficulty with the fact that I have spoiled his world championship party a bit."
Things have not improved since then, and the team heads into the winter with two main priorities: building a worthy successor to the W06 and rebuilding the relationship between Hamilton and Rosberg.
From the outside, Rosberg seems most put-out by Hamilton's behaviour towards him on the track, while Hamilton—who has been more willing to air his grievances in the public domain—appears to be displeased as much with the internal workings of the team as he is with Rosberg.
The Brit has argued over strategy at each of the last three grands prix and has clearly lost patience with Mercedes' "team first" approach—in which the drivers are not allowed to go for significantly different strategies.
He has also commented on how he feels Mercedes have been treating Rosberg—telling a media briefing in Mexico that the team were being "extra-warm" toward the German and were going out of their way to keep him happy.
After the season finale, he added a little more fuel to the fire, telling the BBC that Rosberg "complains about a lot of things" before adding, "It's kind of the different background we come from, I guess."
The breakdown in relations has forced Mercedes team boss Toto Wolff to issue a very blunt warning to the pair. Speaking to Motorsport.com's Jonathan Noble, he revealed the ill-feeling was starting to affect the rest of the team and something needed to change. He said:
We took the decision of having two evenly matched drivers in order to make the team progress faster and better. It was a very conscious decision three years ago.
Going forward, we will consider if it is the best set-up for the team. Personality and character within the team is a crucial ingredient for the team success.
If we feel that it is not aligned with the general consensus, spirit and philosophy within the team, we might consider that when we take a decision, in terms of the driver line-up going forward.
Asked by Noble to clarify whether he meant the team would favour one over the other—or maybe change the line-up—Wolff replied, "I think it is important to have talented and fast drivers in the car. But we want to work with nice guys."
His message is quite clear: they either work together, or one of them will have to go and work somewhere else.
But who should be more worried about Wolff's comments—Hamilton or Rosberg?
The obvious candidate would have to be Rosberg, primarily because he just isn't as good a driver as Hamilton is. The last two years have proved beyond any reasonable doubt that he doesn't have the consistent speed needed to properly challenge his team-mate.
He also appears to lack the cutting edge so often present in champions—evidenced by his poor wheel-to-wheel record against Hamilton—and despite being one of the best qualifiers in the field, his race-day performances are not always first class.
In their three seasons together as team-mates, Rosberg has 13 race wins, 21 pole positions and 10 fastest laps. Hamilton's record stands at 22 race wins, 23 pole positions and 15 fastest laps.
The Brit also has two world championships; his team-mate, of course, has none.
Rosberg shows occasional flashes of brilliance and has the ability to beat anyone on his day, but we, and Mercedes, have seen enough to know that "his day" just doesn't come round often enough.
He's still one of the best drivers on the grid and would be capable of winning a championship as the lead driver in a car with a modest performance advantage over the rest of the field.
But he isn't in the same class as the likes of Hamilton, Fernando Alonso or Sebastian Vettel. Mercedes know that if they didn't produce a superior machine, they could not with any certainty rely on Rosberg to take the fight to the very best drivers over the course of a whole season.
Hamilton, on the other hand, has repeatedly—in 2007, 2008, 2010 and 2012—proved he can do just that.
Finding another driver of Rosberg's calibre or better would not be too difficult. Daniel Ricciardo looks to be at the very least the German's equal, while Valtteri Bottas, Romain Grosjean, Sergio Perez and Nico Hulkenberg would also be worthy of consideration.
So, too, it appears, would be Daniil Kvyat and Max Verstappen—once they have a little more experience.
But Mercedes wouldn't even need to find a driver as good as Rosberg; they could instead decide to leave Hamilton relatively unchallenged for a season or two. This would make their task easier still and open the door to a newcomer such as Pascal Wehrlein or Esteban Ocon to come in and learn the ropes.
Replacing Hamilton would be a much taller order. Where he sits in the "best drivers" ranking varies from person to person, but the drivers whose names are mentioned most frequently alongside Hamilton's are Alonso and Vettel.
They are the two—along with Ricciardo—whom Hamilton himself regards as his strongest opponents.
Vettel is locked down to Ferrari, and it's hard to imagine him wanting to leave or being let out. And if a driver change is being made to ensure team harmony, bringing in a character as strong and demanding as Alonso would be sheer lunacy.
If Mercedes wanted Hamilton out, they could not replace him like-for-like. Their only option would be to take a punt on someone like Ricciardo or Verstappen and hope their new recruit fulfilled his undoubted promise and turned out to be a world-class racer.
And if the team would struggle to replace Hamilton as a driver, they'd find it impossible to fill his boots in another area—marketing appeal.
The three-time world champion is F1's only genuine global megastar. His celebrity lifestyle gives him a level of exposure that far exceeds any of his rivals, and his fanbase is not limited to motor racing fans.
Hamilton is regularly seen on red carpets alongside musicians, models, actors and designers—and he no longer looks out of place. While most sporting stars only ever receive mentions in the back pages of newspapers and on sports websites, Hamilton is one of a select group capable of generating column inches elsewhere.
He is also the driver with, by some margin, the largest following on social media. A Sky Sports F1 study published in September reported his total fan or follower count across Facebook, Twitter and Instagram amounted to around 7.7 million people.
Rosberg had a reach of "just" 2.25 million people. A glance at their respective pages shows Hamilton has added around one million extra fans to his tally since the study was published; Rosberg has increased his following by 400,000.
Every F1-related tweet, post or picture the drivers share with their supporters raises awareness of the Mercedes brand—and the more popular a driver, the more likely a high-paying sponsor will want to be associated with them.
So to a team whose very presence in the sport relies on it being commercially good for them, Hamilton is gold dust; Rosberg—though well-supported relative to most drivers—is not.
Hamilton also has the upper hand when it comes to money. Though he costs more per season than Rosberg, he has a contract that ties him to the team until the end of 2018.
Mercedes would have to pay a fortune to break it, but they could get rid of Rosberg—whose current deal runs out at the end of 2016—for nothing.
But it's not all doom and gloom for Rosberg, because it could be argued that his nationality works in his favour. Germany is the home of Mercedes and remains one of its biggest markets, so the board of directors—if not those in charge of the team—may favour having at least one German in a race seat.
History, both recent and ancient, would support this—from the pre-war days to the present, Mercedes have never entered a grand prix without at least one German driver.
And there are positive benefits to the team of having someone capable of speaking to their "home" fans without the need for a translator.
But it's still hard to imagine Mercedes putting nationality ahead of success, worldwide marketing appeal and money.
And even if they did, Rosberg isn't the only German driver available. Hulkenberg, whose profile was raised significantly by his Le Mans victory, fits the bill, and in Pascal Wehrlein, Mercedes have a young German with plenty of potential.
Working purely from comparisons between the two, it's very difficult to look beyond Rosberg as the driver under threat. He's easier to replace in terms of talent, his marketing appeal is substantially lower than that of Hamilton, and it would cost Mercedes nothing to dispense of his services at the end of 2016.
He knows that, and Hamilton does as well—and it's possible that rather than working to ease tensions, Wolff's words could give the Brit some extra leverage in his psychological battle with Rosberg.
But it would be unwise for Hamilton to consider himself entirely safe, because Mercedes have always been very clear that no driver is bigger than the team.
His talent is prized, his global celebrity status makes him a very valuable asset and his lengthy contract makes him expensive to sack. But the Mercedes team is just a tiny part of Daimler AG—a company that reported 2014 revenues of almost €130 billion.
Should it be decided Hamilton is not being the team player Mercedes want him to be and his presence is disrupting the team, Daimler could probably find the money to send him on his way.
So while Rosberg has the most to worry about, Hamilton has at least a little reason to be fearful.