In typically humble and understated fashion, José Mourinho recently described his Real Madrid side, which were eliminated in the 2011/12 Champions League semi finals by Bayern Munich, as the 'best in Spain and also the best in Europe'.
While the former Chelsea boss has been prone to self-important outbursts in the past, it is pretty difficult to dispute this particular claim.
During the 2011/2012 campaign, Los Blancos (feat. Sergio Ramos, Xabi Alonso, Mesut Ozil and of course Cristiano Ronaldo) temporarily halted the best Barcelona side in history's reign of terror, lifting La Liga title and scoring a record 121 goals in the process. Therefore, falling short on the European stage must have been a crushing blow.
Here are seven of the very best, who like Madrid, might have been dominant domestically and on paper but just could not deliver on the continental stage...
It might seem (very) strange to say now but for a short period back in the early 90s, Walter Smith's Rangers were the best British team...by some distance.
1993 marked the rebrand of the European Cup to the Champions League and the Gers (who had done the domestic treble) almost went all the way to the final - seeing off the likes of English champions Leeds and Russian powerhouses CSKA Moscow in the process.
Super Ally McCoist and co eventually failed to earn a date against Fabio Capello's Milan in the final, after finishing second in the second group phase to eventual winners Marseille. Tthey drew twice against the French side, who would soon be embroiled in a domestic match-fixing scandal.
Rangers continued to dominate domestically until the late 90s but have failed to replicate their European heroics since.
So near and yet so far. Valencia twice reached the Champions League final at the turn of the century and twice lost - to Real Madrid and then Bayern Munich.
While they were outgunned in those two finals, it is actually (ironically) the season after in which they were probably the best in Europe.
Rafa Benitez toke over Hector Cuper's nearly men and took them to domestic glory in La Liga in 2001/02, with a team featuring absolute hipster porn like Roberto Ayala, Ruben Baraja and Pablo Aimar.
Zinedine Zidane's volley stole the show in the 2002 final but Valencia had finished a full eight points clear in La Liga.
Rafa's defence-first machine would go on to lift the UEFA Cup in 2004, but they never tasted Champions League glory.
Going a full Premier League season unbeaten is mightily impressive. It's basically impossible.
It's just a shame that Arsenal failed to replicate this success on the continental stage during the 2003/04 campaign.
The Gunners were unequivocally the continent's in-form team when they crashed out of the Champions League to London rivals Chelsea in the quarter-finals, with Wayne Actual Bridge of all people scoring the winner in the second leg at Highbury.
After the game, Wenger blamed the defeat on his players being too scared to make a mistake going forward.
Whatever the reason for Arsenal's failure, the result was a bitter blow to the Invincibles' legacy.
Chelsea 2005 - 2006
Chelsea's domestic dominance was undisputed in the two seasons following 'Special One' José Mourinho's arrival at the club in June 2004.
They set records on the pitch and in the transfer market on their way to their first league titles in decades but faltered in Europe, with Liverpool (famously) knocking the Blues out via a Luis Garcia goal that may or may not have crossed the line on their way to the 2005 final.
One year later, they would only reach the round of 16 with familiar foes Barcelona narrowly beating them over two legs.
For all Mourinho's early success, not conquering Europe with Chelsea remains an eyebrow-raising omission from his CV.
Atletico Madrid 2014 - 2016
They may not have been the most attractive team to watch but Diego Simeone's Atletico Madrid side were ruthlessly effective between 2014 and 2016.
During that time, Atleti won La Liga in an era dominated by Barcelona and Real Madrid and reached the Champions League final twice...but fell at the final hurdle to their city rivals on both occasions.
As if that wasn't punishment enough, both games were also decided by the narrowest of margins, with Los Blancos requiring extra time in 2014, before winning on penalties two years later.
To add further insult to injury, Atleti had taken four points from six against Real in the league in both 2013/14 and 2015/16.
Juventus 2015 - 2019
Since 2011 Juventus have won eight successive Serie A titles but European success has (somehow) proved elusive.
The Old Lady have reached two finals during this time, falling short in 2015 and 2017 to both of Spain's super-clubs, Barcelona and then Real Madrid.
More recent times have also been characterised by disappointment with Cristiano Ronaldo's acrobatic bicycle kick (and Michael Oliver's bin heart) ending their hopes in 2018.
Relative minnows Ajax then knocked out the favourites in the quarter-finals last season, despite the introduction of Ronaldo in Turin.
Manchester City 2016 - Present
Pep Guardiola has built a glorious footballing dynasty since taking over at Manchester City in 2016. Premier League records have fallen like dominoes but the Champions League has proven to be a much tougher nut to crack.
After making the semis in 2016 under Manuel Pellegrini, their lowest ebb was elimination to Monaco in Guardiola's inaugural campaign but bowing out to finalists Liverpool and then Tottenham in subsequent years has also been really, really disappointing.
With the Citizens banned from the competition for the next two campaigns, they will likely not be ending their Champions League hoodoo any time soon.