When Jose Mourinho returned to Stamford Bridge in the summer of 2013, there was a feel-good factor that for all the millions Chelsea have spent since the turn of millennium couldn't have bought.
A year later, Chelsea were Premier League champions again. It seemed like the Special One would never leave west London and the glory days - with the great team he had assembled - looked like they were here to stay for the foreseeable future.
Then it all went wrong.
Before anybody knew Leicester would win the league and then battle relegation the following season, Chelsea had the most spectacular demise as champions in living memory.
Even up until Christmas, they were within striking distance of the bottom three. Needless to say, Mourinho was sacked.
Fast forward to today and Mourinho is the boss at Manchester United and has just won the EFL Cup while Chelsea are 10 points clear at the top of the Premier League under Antonio Conte.
The former Real Madrid and Inter Milan boss is set to return to Stamford Bridge on Monday night as his United side battle the Blues in an FA Cup quarter-final.
The last time the 54-year-old came home to the Bridge, the Red Devils were humbled 4-0 and Mourinho was left embarrassed.
However, a lot has changed since then. In fact, United have not lost in the league again since that fateful day last October and their unbeaten run currently sits at 17.
Things appear to be on the up at Old Trafford, but what went so wrong at Chelsea after such a glorious first season back?
It's a question we've all wondered many times, but Gary Lineker finally got the chance to ask it on behalf of Football Focus, as you can from the video below.
It's a classy response from the Portuguese tactician and he has been careful not to cause a war ahead of the crunch clash on Monday.
With a place at Wembley at stake, Mourinho's men will have to recover from their trip to Russia on Thursday while Chelsea have had a full seven days to prepare after their victory at West Ham.
Either way, judging by Mourinho's expression, there is clearly plenty more to say on the matter.
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