Brock Lesnar made an astonishing return to WWE on Night Two of the 2025 SummerSlam. The Beast Incarnate attacked John Cena right after he lost the Undisputed Championship to Cody Rhodes in a Street Fight. Fans are still guessing Lesnar's true motives behind this attack. However, there is a chance that The American Nightmare is the man behind sending the former three-time Universal Champion after Cena.Cody Rhodes is getting revenge for his WrestleMania 41 humiliationRhodes' defeat at WrestleMania 41 was a low point in his career. He failed to protect the title he had won after over two years of hard work and fighting The Bloodline. Moreover, the 'Mania defeat was humiliating for him, since one of the key factors for his loss was the intervention of Travis Scott.Brock Lesnar was last seen in WWE at the 2023 SummerSlam, where he lost to Cody Rhodes. After the bout, The Beast Incarnate acknowledged The American Nightmare and raised his hand as a sign of respect. Thus, the new Undisputed Champion could have used his friendship to unleash Lesnar on Cena, to make him pay for tarnishing his title run.Cody Rhodes has been showing heel tendenciesCody Rhodes hasn't been the same since his return to WWE in the May edition of Saturday Night's Main Event after a big hiatus following WrestleMania 41. The American Nightmare has been seen using several heel-coded tactics to win his matches.Sure, he saved his friend, Jey Uso, from an ambush on two occasions. But as Randy Orton had pointed out after his King of the Ring finals defeat, Rhodes didn't hesitate to use the exposed turnbuckle to his advantage to win the match at Night of Champions.Moreover, he didn't let John Cena get away with trying to forfeit a match at SummerSlam, ramming the Undisputed WWE Championship belt in his face. He then forced The Franchise Player to sign the contract, without disclosing that the title match included a Street Fight stipulation.All of these things point to a darker character shift, which makes it possible that he sent Brock Lesnar after John Cena. While this is a possibility, all of this is speculation so far.Brock Lesnar is one of the few rivals John Cena has failed to overcomeJohn Cena was the face of WWE for almost two decades and the entirety of the PG Era. While The Leader of Cenation dominated almost all his rivals during this period, Brock Lesnar is one of the few men he got crushed under instead. The Beast Incarnate has a 4-2 head-to-head lead on The Franchise Player. Moreover, one of John Cena's wins against Lesnar was the result of a disqualification. Now the former three-time Universal Champion has returned and rekindled his rivalry. Exactly 11 years ago, at the 2014 SummerSlam, Lesnar even dominated Cena, sending him to Suplex City a total of 16 times to win the WWE World Heavyweight Championship. It would be interesting to see what happens next in John Cena's retirement tour after The Beast Incarnate's comeback.