IT'S a feud that's threatening to blow PSG apart.
Superstars Kylian Mbappe and Neymar's frosty relationship came to a head when they clashed during a 5-2 win over Montpellier - with Mbappe demanding Neymar hand over penalty duties to him last month.
When the French World Cup winner didn't get what he wanted, he seemingly threw a strop on the pitch.
To top it all off, Mbappe missed a penalty before Neymar stepped up and converted another later in the game, despite Mbappe's pleas to take the second spot kick as well.
After the game, Neymar appeared to like a pair of tweets criticising Mbappe's apparent role in the team as the main penalty taker.
And that's not the first time we've heard of unrest in the PSG camp. In the past, Neymar has been accused of comparing his strike partner in looks to Teenage Mutant Ninja Turtles cartoon character Donatello.
Mbappe has admitted all is not well between the pair - and said because they are strong characters they won't always see eye-to-eye.
Mbappe said: “This is the sixth year with Neymar.
“We have always had a relationship like this, based on respect, but sometimes with warmer and colder moments.
“It is the nature of our relationship. I have a lot of respect for the player that he is.
“When you have two players with such a strong character, you have moments like that, but always with respect and in the interest of PSG.”
Talk of a rivalry began almost immediately following Mbappe's permanent £162million move from Monaco.
In 2018, Mbappe was fuming that Neymar didn't pass the ball to him during a 1-0 win over Toulouse.
It reportedly escalated into a dressing room bust-up - where shocked team-mates had to separate them.
Heroes in a half shell
Behind-the-scenes, Mbappe was also said to be on the receiving end of mickey-taking from PSG's Brazilian contingent - with Neymar the ringleader.
After a Champions League game against Celtic a year earlier, when Mbappe was on loan with the Ligue 1 giants, Neymar and Dani Alves attempted to goad him into eating some pizza on the team bus.
"Donatello, have some pizza! Eat some!" Neymar and Alves joked as they laughed at their gag.
El Pais later claimed Mbappe's mum Fayza was uncomfortable at the way the teen striker is persistently teased and compared to Teenage Mutant Ninja Turtle Donatello.
Ex-PSG defender Alves also posted a photo of Donatello after Mbappe scored twice in France's 4-3 win over Argentina in the last-16 at the 2018 World Cup.
While, the same year now Chelsea centre-back Thiago Silva gave the forward a mask of the character as an early Christmas present.
Fayza felt the joke had gone too far, and in essence it does feel like a school bullies in the playground like situation.
Mbappe was believed to have been fed up at being the butt of the joke too, understandably.
Boiling point
This season, new PSG manager Christophe Galtier made it clear.
Mbappe was to be the No1 penalty taker, while Neymar would be No2 - in the case of Mbappe not being on the pitch.
Clearly, Neymar wasn't happy with that decision. After Mbappe missed a 21st minute against Montpellier in the first few weeks of the season - they were awarded another 20 minutes later.
Neymar immediately grabbed the ball, much to his team-mate's surprise, and wouldn't let Mbappe have the ball.
They had words right before Neymar stepped up and scored, but the ex-Barcelona ace wasn't listening.
Mbappe sulked on the pitch for the rest of the match. It wasn't pretty.
PSG chiefs took action the next week. Both were hauled in for showdown talks to iron out their differences.
Astonishingly, Neymar was then reportedly offered out to clubs for a last-minute summer transfer.
Manchester City turned down the opportunity to sign the Brazilian.
Isolation and empty promises
And Chelsea also opted against bringing him to the Premier League.
It's no secret Mbappe wants Neymar out of PSG.
All in all, Mbappe feels let down and "isolated".
In the summer, with his future up in the air, he committed himself to PSG and was awarded with a mega £300million deal.
With that came some assurances. Mbappe would be able to have his say on elements of how the club is run.
AS claimed Mbappe would be given the opportunity to take all of the team's penalties and have power over club decision-making in transfers and appointments.
The report added Mbappe's new-found power has caused a rift between him and some of his team-mates, leaving him feeling "isolated."
Mbappe has also been left "disappointed" with the club failing to sell Neymar, a move he did not object to.
Of course, that didn't happen. Now they have to find a way to make it work.
If they do, they should - on paper at least - be the most fearsome forward line in world football.