Only twice before have Arsene Wenger and Jose Mourinho done transfer business with one another.
In 2006, Ashley Cole made the switch from north to west London in a deal worth £5 million, with William Gallas heading in the opposite direction.
And last year, in the 2015 transfer window, Petr Cech completed a sensational £10 million move to Arsenal after being displaced as Chelsea's No.1 goalkeeper by Thibaut Courtois.
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Wenger doesn't like doing business with Mourinho and vice versa, it's as simple as that.
However, according to the Mirror, that could all be about to change.
They claim that Wenger has been alerted to Chris Smalling's situation at Manchester United and is lining up a move for the England international.
Smalling's recent debacle with Mourinho, where the Portuguese manager slammed him for pulling out of last weekend's game against Swansea City, appears to have put his future in doubt.
"There is a difference between the brave, who want to play at any cost, and the ones for whom a little pain can make a difference," Mourinho said in a post-match interview.
"For the team, you have to do anything."
Wenger could now swoop for Smalling as a result, with the Frenchman a long-term admirer of the 26-year-old having failed to sign him in 2010.
Smalling would instead join United for £10 million, where he has since developed into one of the Premier League's best centre-backs.
The Mirror's report is worth taking with a pinch of salt, though. Wenger signed Shkodran Mustafi for £35 million in the summer, so he's not exactly desperate for another defender.
But then again, with Laurent Koscielny now 31, perhaps Arsenal's veteran manager regards Smalling as the France international's ideal successor.
Who knows, but one thing's for sure: Smalling wouldn't come cheap.
English players are already overpriced and, were Mourinho to genuinely consider cashing in, he would likely set a ridiculous asking price somewhere in the region of £30-£40 million.
After missing out on Smalling six years ago, Wenger expressed regret at not being able to beat rivals United to his signing.
"I am sorry because we were very close to getting him," he told Arsenal's official website. "We were on the case very early.
"I wish the player well. At the end of the day it is important he has a good career. In both clubs he has a good chance to make a great career. The most important thing is he does that."
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