Jose Mourinho endured a nightmare return to Stamford Bridge on Sunday as his Manchester United side were soundly beaten 4-0.
Goals from Pedro, Gary Cahill, Eden Hazard and N'Golo Kante meant Antonio Conte's men walked away with the three points and climb into the top four.
The Red Devils boss lamented the 'incredible defensive mistakes' that gifted his former team's goals - particularly the opening two in the first half - and Mourinho cut a frustrated figure on the touchline throughout the 90 minutes.
At the end of the game, Mourinho extended the traditional handshake with his opposite number Conte beyond the normal conventional time to say something in the Italian's ear.
You can watch the encounter below although it is difficult to make out what is actually being spoken but the expression on Mourinho's face suggests it wasn't exactly complimentary.
Speculation surrounding the conversation has been rife but it has been reported that Mourinho took exception to Conte's antics on the touchline during the game.
Gazzetta Dello Sport journalist Filippo Ricci and The Times' Gabriele Marcotti have both tweeted, believing the Man United manager said: "You don’t wind up the crowd at 4-0. You do it at 1-0. It’s humiliating.”
That's after Conte was seen urging the Chelsea fans to become more vocal at one stage during the second half even though the match was already won.
Regardless of what Mourinho said, it will be the standard of his players' performances that will be of most concern.
The Portuguese boss was heavily criticised for his negative tactics during the 0-0 draw with Liverpool last Monday and he arrived at his old club with a slightly more open setup.
But he was brutally punished by a clinical Chelsea side and Mourinho will now need to re-evaluate the direction he plans to take Man United in the short-term.