Professional wrestling and MMA have rubbed shoulders for decades, with athletes crossing between disciplines, but never before have the two worlds been as united.
Following the news that WWE and UFC have merged under Endeavor Group Holdings, critics and fans are speculating about the direction the newly formed £17.3bn sports entertainment brand will take.
Many details are unknown, but BBC Sport looks at why the deal may make sense, the reaction, and what it means for the worlds of MMA and pro wrestling.
The key difference between the UFC and WWE lies in competition.
The UFC is a competitive sport where athletes fight to determine a winner by knockout, submission or decision, whereas the WWE is classed as 'sports entertainment', where winners of bouts are pre-determined with storytelling at the heart of its ethos.
Despite this, there are similarities between the two, and this is thought to contribute to a crossover in fans which could be a key factor behind the deal.
Many athletes from WWE and the UFC have collegiate wrestling backgrounds with the sport providing a strong base in both disciplines.
This has seen athletes like Shamrock, Lesnar, Jake Hager and more have successful careers in both.
There are also a number of UFC fighters who have referenced the outspoken and flamboyant stars of WWE as being influential in their growth as entertainers, which in turn helps the promotion of fights.
These include Rousey, who left the UFC to go on to become a WWE champion, Colby Covington who regularly adopts WWE themes for his cage walk, and Israel Adesanya.
Former UFC middleweight champion Adesanya fights Alex Pereira in a rematch for the title at UFC 287 in Miami, Florida on Saturday.
"Maybe I didn't realise how big an influence [WWE was]," Adesanya told BBC Sport.
"As an entertainer it definitely played a part. I spent Fridays watching [WWE promotion] Smackdown, Mondays watching Raw and watching these guys do their thing, being charismatic and electrifying, on the mic and in the ring.
"We used to practice the crazy moves too, doing the Hardy Boyz' Swanton Bombs off the couch armrest on to the mattress. That played a part definitely in shaping me I guess into the man you see before you."
The importance of the self-promotional side of MMA, which is heavily influenced by pro wrestling, is emphasised by the UFC's record pay-per-view numbers.
The outspoken Conor McGregor dominates, featuring in eight out of 10 of the most-bought UFC shows of all time, but record cards without the Irishman include Lesnar, Rousey and Jorge Masvidal.
A closer look at the inner workings of the UFC also shows similarities to pro wrestling.
Like in WWE, the UFC sometimes creates bouts with storytelling at the heart of its promotion rather than making fights between close-ranked athletes.
For example, Pereira was granted a shot at Adesanya's title in November after only three fights in the UFC because of history between the pair, with Pereira earning two prior wins over the Nigerian in kickboxing.
And last February, Masvidal and Covington also headlined an event with no title on the line because of a friends-turned-rivals story arc.
What has the reaction been like?
The business will be led by Endeavor chief executive Ari Emanuel, with WWE executive chairman Vince McMahon fulfilling the same role at the pro wrestling organisation and Dana White remaining UFC president.
White is predicting a fruitful partnership between the three.
"Vince is a savage in the wrestling space, Ari is a beast at what he does, and then add what we at the UFC bring to the table and there is no limit to what this company can accomplish in the next few years," said White.
Some have been wondering what effect the deal will have on fighter pay in the UFC.
The UFC's contractual rules mean fighters are constricted when it comes to making money from promotional deals while fighting inside the octagon, with some, including former heavyweight champion Francis Ngannou, leaving the organisation to seek "freedom".
Elsewhere, people have been speculating about potential athlete crossovers, although it is more likely UFC fighters will make cameo appearances in WWE rather than wrestlers fighting inside the octagon.
McGregor has already thrown his hat into the ring...
It is unlikely there will be any drastic changes to the look and feel of each branch, with the merge likely creating more opportunities for brand enhancement and crossovers behind the scenes.
One example of this is already in motion with YouTuber and WWE star Logan Paul's energy drink Prime being promoted across the UFC and WWE.
The merge could see scheduling unison between the UFC and WWE, with the pair perhaps unlikely to host events at the same time in order to preserve ratings, while advertising one another's shows.
Another change which could take place is more similarities in how each brand is broadcast.
At present the UFC uses a pay-per-view model in the US, while WWE houses all its content under its streaming service the WWE Network, with both branches having a deal with BT Sport in the UK.
BBC
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