Rafael Nadal's reaction said it all.
A poignant scene that was as heartbreaking as it was heartwarming played out at the O2 Arena as legends demonstrated their respect for the greatest to ever pick up a racquet.
Nadal's tears were a clearer picture than any testimonial or tribute could paint about the loss the sporting world - not just the tennis world - felt as Roger Federer said an emotional farewell in the early hours of Saturday morning.
This was Federer's greatest rival. The most successful men's player in Grand Slam history. The man against whom Federer had enjoyed and endured his most defining matches and the most defining period of his career.
Without Nadal in his way, Federer's tally of 20 Grand Slams would be much bigger, the Spaniard beating the Swiss maestro in six of their nine Grand Slam finals and 10 of their 14 Grand Slam meetings overall.
Likewise, Nadal's already-record tally of 22 Grand Slams would be further clear of Novak Djokovic, the only other serious contender to the crown of the greatest ever, without Federer's presence at the top of the game for so long.
Yet the respect and love Federer and Nadal have for each other meant that the Spaniard looked every bit as devastated at Federer leaving the sport as the retiring icon himself.
In no other sport, and no other rivalry, would that be the case, and it speaks to the reverence in which Federer is held that his retirement was treated almost like a funeral - albeit one with laughs, entertainment and some final glimpses of magic before the tears arrived.
An SW19 swansong may have been the dream for the eight-time Wimbledon champion - for once the Swiss clock was inaccurate when ticking down on Federer's career in that regard - but Friday's Laver Cup spectacle was a suitable substitute.
A 1,383rd career win from his 1,750th match would have been nice, but even the defeat, thrilling as it was, could not dampen the occasion as Federer was given a fitting farewell in the city he has forged a stronger connection with than any other, and alongside his great friend and rival Nadal.
The statistics behind his legendary career have been well worn since he announced his retirement last week: 20 Grand Slam titles, 310 weeks as world number one - including 237 consecutively - and 103 ATP Tour triumphs among them.
It is not the numbers which will define Federer, though; instead, it is the way he made people feel when he played the sport.
Federer does still lead the way in many metrics, but in others - including the headline figure of Grand Slam titles - he already trails his two great contemporaries Nadal and Djokovic.
With an inferior head-to-head record against both players too, a purely statistical look at the GOAT debate in tennis would rarely conclude with Federer standing above the rest.
However, many of those who were lucky enough to witness him in his prime - and there are a few different periods of his career which would compete for that title - hold Federer up as untouchable, even above the already-legendary feats of Nadal and Djokovic.
Federer came closer to achieving that holy grail of pristine sporting perfection than perhaps anyone else in sporting history. He played the game more beautifully than anyone before or since, with his balletic style of class and grace raising countless goosebumps and hairs on the back of the neck.
As already alluded to, it is impossible to fully extract Federer's achievements from those of the others in the Big Three; they pushed him to even greater heights, and vice versa.
However, neither Nadal or Djokovic, for all of their greatness, have made as many jaws drop or raised as many people out of their seats in ecstasy as the Swiss master.
Federer's almost dismissive one-hand backhand and his finely finessed forehand are iconic strokes, and the thought of never seeing them in professional tennis again is yet another tug on the heart strings of sports fans worldwide.
The thought of there never being another battle between Federer and Nadal - two men who along with Djokovic have dominated the sport for the best part of 20 years - is difficult to comprehend.
Arguably sport's greatest ever rivalry is now over once and for all, the contrasting styles of both players making for some of the best sporting spectacles we have ever seen as Federer's ice met Nadal's fire.
The 2008 Wimbledon final is a match no-one who watched it will ever forget, and it is perhaps cruel that such a huge part of Federer's legacy ended in defeat on that dusky London night.
Yet, as with the statistics, Federer's legacy transcends even victories and defeats. His level of success is of course the driving factor behind his GOAT claims, but his grace both on and off the court is the deciding factor for many when compared to his rivals.
It is difficult to think of a more universally revered, respected or loved athlete in the history of sport.
It helps, of course, that tennis is mostly an individual sport without the tribal loyalty which is prevalent in team sports like football. There are those firmly in the Nadal and Djokovic camps when it comes to the GOAT debate, but you will be hard-pressed to hear a bad word said about Federer from fans, players, pundits or anyone else.
We have been blessed to live in an era where many sports have produced contenders to be the greatest ever, yet even the likes of Lionel Messi, Cristiano Ronaldo, LeBron James, Tom Brady and Lewis Hamilton somehow still have plenty of detractors.
Tiger Woods is perhaps the closest, having also forged a legendary career in an individual sport, but his well-publicised off-field issues have detracted from his overall image, whereas Federer has kept his pristine throughout his 24 years as a professional.
If any of those fellow greats - or Nadal or Djokovic, for that matter - retired tomorrow then there would be a similar outpouring of eulogies in recognition of their achievements, but there would unlikely be such a unanimous outpouring of love or feeling of loss all over the world.
Federer's position in the pantheon of all-time sporting giants has been beyond debate for some time now - he is right up there with the likes of Don Bradman, Muhammad Ali and Michael Jordan, and deserves to be included in any debate as to who is the very best athlete in sports history.
If anything, his position in the tennis GOAT debate is murkier than his standing beyond the sport thanks to the presence of Nadal and Djokovic, but for me and millions of others, he still stands above the rest. There will never be another like Roger Federer.
Thank you, Roger!