To think, there's directors at Chelsea who questioned Conte and his text last month. They wanted to call him away from his summer break. Demand he front up to the board. Explain himself. The millions he'd cost the club. The treatment of poor, little Diego. But now...?
It was claimed Diego was ready to heal wounds. To mend bridges. He still wanted to play for Chelsea - and for the manager. But excused from the first days of preseason, Diego didn't get his head down. Back home in Brazil, in Lagarto, he partied. And via Instagram, he made sure Conte, his teammates - even Roman Abramovich - knew about it.
So much for an olive branch. Diego snapped his in two and stomped all over it. On his live feed, as Blues pals had just finished a day's training, Costa updated everyone on the party he was attending. They saw drinking, dancing. Okay, no problem. But then Diego turned the camera on himself - and there he was, wearing an Atletico Madrid shirt. A taunt? An insult? How else could you read it? With Chelsea and Atletico in very public negotiations over the striker's future, he might as well have flicked the V-sign at those watching on.
Oh, and it didn't stop there. Cesc Fabregas was among those logged into the feed, posting a laughing emoji at the sight of Diego in his shirt. His response? A message for the manager: "give Conte a hug". It dripped of sarcasm.
This was Chelsea's big weekend. After a slow transfer window thus far, they'd finally managed to get Tiemoue Bakayoko's deal over the line. Bouncy. Upbeat. The lad's a big character. Sure to be a fans' favourite. Monday morning, we should all be talking about the former AS Monaco man and where he'll fit in Conte's plans. And he has the patter, name-checking Didier Drogba and Claude Makelele among his influences. Hailing N'Golo Kante. He's been channeling the best of John Terry since Friday.
But all that positivity has been engulfed by Diego Costa and his antics. Again.
And put the shirt to one side. Let's not forget, this is the same Diego two summers ago who, by his admission, returned late to preseason training overweight and undermotivated. Today? Well, all we see from the striker is parties and quadbikes. Clearly, Conte could sense history repeating itself. It might be difficult for some to accept inside the boardroom, but the Italian actually knows a little about footballers and their habits.
Diego has been great for the Premier League. No doubt. He's theatre. Tickets are sold because of him. A good footballer, but a great act. You can't take your eyes off him. Who's he arguing with? Why's he waving his arms around? Is he going to retaliate? The drama that swirls around him. Forget the football. It's Diego the character who's the headliner.
When that return to Madrid is rubberstamped, we'll miss him. Maybe not Conte. But many will. Controversial. Entertaining. And with a decent first touch. Diego Costa epitomises the Premier League.
But for Chelsea. For Conte's Chelsea. Sunday's antics belonged to a different era. To that of JT, Drogba and Frank Lampard. A time when the players not only challenged authority, but mocked and ridiculed it. AVB. Scolari. Rafa. They all tried to stand up to them - and were swept away.
A couple of years ago, Diego's behaviour would've been celebrated inside the club. Cesc's post is proof of that. But those days are over. The Lagarto feed the last throes of a bygone era.
On the continent, they talk about cycles. And at Chelsea this is Conte's cycle. He knew exactly what he was doing with that cannonball text. And Costa, on Sunday, just proved him right.