Teddy Atlas says promotor Al Haymon likely will keep the belts in the family, having his own fighter Andy Ruiz Jr. take on one of his other clients, like Deontay Wilder. (1:10)

Andy Ruiz Jr. did what many believed was the impossible by stopping Anthony Joshua in Round 7 on Saturday to capture the WBA, WBO and IBF world titles in one of the biggest upsets in boxing history.

So what happened, and what did we learn?

1. Ruiz won -- did boxing lose?

Anthony Joshua, down, lost his titles and his cloak of invincibility against Andy Ruiz Jr. Mark Robinson/Matchroom Boxing UK

It wasn't just Joshua who suffered a defeat. Deontay Wilder was a big loser too. While Wilder might eventually face Joshua in the future, that fight will never have quite the same importance or buzz as it did for the past year, when both were undefeated heavyweight titleholders.

Before this fateful weekend, if you had asked most boxing fans, both hard-core and casual, which fight they would most like to see in 2019, the answer probably would have been Joshua vs. Wilder. And now, after all the public posturing and promotional machinations that took place between the two sides, the two fighters and fans alike are now left with the possibility of nothing.

This was somewhat reminiscent of another monumental heavyweight upset -- when James "Buster" Douglas defeated Mike Tyson in February 1990. Sitting ringside that night in Tokyo was Evander Holyfield, who was waiting in the wings for Tyson to take care of business so that Holyfield could face "Iron Mike" for an eight-figure payday in what would have been a matchup of two well-known and undefeated heavyweights in their physical primes.

ESPN Stats & Information

A pairing between Joshua and Wilder as undefeated heavyweight champions would have been one of the rare events in which boxing would've taken center stage on an international level.

Perhaps Wilder is finding a sense of satisfaction out of all this, given the acrimony of what has been an all-too-public negotiation with Joshua. But there has to be a part of him that is frustrated that the opportunity to be the first man to make the London Bridge fall down has evaporated, along with a career-high payday.

Once again, the business of boxing got in the way of the sport.

2. Is Joshua's chin a problem?

Joshua was down four times during his TKO loss to Ruiz. Ed Mulholland/Matchroom Boxing UK

At this point, it seems like a rhetorical question.

What looked to be an early night for Joshua after flooring Ruiz in Round 3, instead became the beginning of a Gotham City nightmare in Joshua's United States debut. As he came into close the show on Ruiz, Joshua was caught by a series of crisp counterpunches from Ruiz, who proved he too could punch.

Ruiz-Joshua: Things to know Ruiz: First heavyweight champion of Mexican descent

Ruiz: Had lost his only previous world title fight in 2016 vs. Joseph Parker (Parker then was beaten by Joshua after two defenses)

Ruiz: Took the fight on two months' notice (was a +1100 underdog in the fight, per Caesars Sportsbook)

Ruiz: Last fought on April 20; 42-day turnaround before challenging for the heavyweight belt is the fifth shortest in the past 50 years

Joshua: Was making his U.S. debut

Joshua: Outlanded 39-23 by Ruiz in power punches (knocked down four times)

Joshua: Entering the fight, he was No. 1 in ESPN's heavyweight rankings (No. 9 in the pound-for-pound list); Ruiz was unranked ESPN Stats & Information

Joshua was stunned by a left hook to the temple during an exchange in the same round and went down in an stunning turn of events. And then once again. And while he survived the round and had some moments thereafter, from that point on, he looked unsteady on his legs and more than that, unsure of his own durability.

Never had a man so strong looked so fragile.

It was an easy call for referee Michael Griffin. While Joshua was on his feet standing on a neutral corner after being knocked down twice more by Ruiz in Round 7, he had symbolically waved the white flag.

And while the result is surprising, the fact is that Joshua was buzzed numerous times, and he hit the canvas four times. We have seen that before. He was stunned in victories over Dillian Whyte and most recently against Alexander Povetkin. Two years ago, Joshua was knocked down by Wladimir Klitschko before stopping Klitschko in a great fight.

For all of his talent, it's clear that Joshua's chin is a flaw. Perhaps it was just a matter of when it was going to be totally exposed.

3. So, who's the best heavyweight in boxing right now?

Ruiz scored a huge upset over Joshua, but is Ruiz the best heavyweight in boxing? Nick Potts/PA Images/Getty Images

While Ruiz has three belts around his waist, does this make him the best big man in the world?

It's not Ruiz, no. But he'll certainly get the opportunity to state his case in the coming months.

WBC belt-holder Deontay Wilder and lineal champion Tyson Fury -- who fought to a contentious draw in December at Los Angeles' Staples Center -- are considered the two best after tonight.

It was announced Friday that Wilder and Fury had agreed to a rematch in the first part of 2020. The winner of that bout will be considered the best fighter in the division. But based on the events we just saw, let's not assume anything just yet. While Wilder will be facing Luis Ortiz in September, Fury still has to fight Tom Schwarz on June 15 and might have another fight in the fall.

Let's not just pencil in this rematch just yet.

4. Is an immediate rematch a good idea for Joshua?

Referee Michael Griffin stopped the fight after Joshua suffered two knockdowns in Round 7. Melina Pizano/Matchroom Boxing UK

The reality is that Joshua has never been the same aggressive attacker post-Klitschko. Now, in the aftermath of his New York meltdown, you wonder if he'll ever be the same. Losses of this nature can affect a fighter more psychologically than physically.

This just seems like a soul-crushing loss for Joshua, and the shiny veneer that accompanied him into this event might never be recaptured. The cloak of invincibility on Joshua had been fading, and now it's completely ripped to shreds.

If they do it again in six months, Ruiz, you would think, would come into the rematch with more confidence -- and at least the same power -- while Joshua will have the same doubts that he left the ring with on Saturday.

In the United Kingdom, Joshua is still a very bankable commodity, but another loss to Ruiz most likely would reduce his status to being the modern-day Frank Bruno.

5. Do we need to give Ruiz credit?

play 2:23 Atlas: Ruiz 'just wrecked a hundred years of physical fitness' Teddy Atlas says that Anthony Joshua didn't look interested in the fight vs. Andy Ruiz Jr. and gives credit to Ruiz for catching Joshua behind the ear, throwing off his equilibrium.

Yes, absolutely. While there is a natural inclination in these circumstances to always talk about the shortcomings of the favorite who loses a fight in this manner, credit does have to be given to the victors for what they achieved.

Ruiz was a late replacement for Jarrell Miller and a more seasoned fighter with a better track record coming into the bout. While neither had faced "great "opposition, Ruiz's only loss in 33 previous fights was a razor-thin majority decision to Joseph Parker in Auckland, New Zealand, for the WBO heavyweight title in December 2016.

Talent has never been an issue for the 29-year-old Ruiz, who despite his less-than-chiseled physique is a boxer who possesses fast hands and fluidity. He will never have rippling abs or the shredded musculature of his colleagues, but he does have natural fighting ability.

He also showed a fighter's mentality by dusting himself off the canvas in the third; instead of getting caved in by Joshua, Ruiz turned things around in dramatic fashion, then proceeded to patiently walk down the defending champion.

Bottom line: Ruiz fights better than he looks.