WWE SummerSlam 2025 Night Two ended with a shocker as Brock Lesnar finally returned to the Stamford-based promotion after two years of absence from television following the controversy.The Beast Incarnate came back after Cody Rhodes defeated John Cena and left the ring with the undisputed title. Lesnar walked around the ring, jumped right inside, and hit an F5 on the Leader of the Cenation.In this listicle, we look at three reasons why Brock Lesnar attacked John Cena at SummerSlam 2025:#3. The Rock's new championJohn Cena abruptly turned babyface at the go-home edition of Friday Night SmackDown before The Biggest Party of the Summer. The Last Real Champion thanked Cody Rhodes for a wake-up call and even took shots at The Final Boss for manipulating to turn heel to produce shocking television.Furthermore, Cena stated that, after he turned evil, everyone left him alone. The callout by the Greatest of All Time may have hurt The Rock's ego, who might have sent his ultimate champion, Brock Lesnar, to hunt Cena down.#2. Mega WWE match to return for the second timeCena and Lesnar have a massive history, having multiple five-star classic matches against one another at different stages of their illustrious career.The Cenation Leader was Brock Lesnar's first feud upon his return to WWE in 2012. Both are decorated legends from the Ruthless Aggression era and could face off in a superfight in "End of an Era" 2 later this year.#1. Double retirementBrock Lesnar and John Cena are both legendary and have had impactful careers, and they have nothing to gain from the Stamford-based promotion. Mr. Hustle Loyalty and Respect will retire later this year.Shockingly, it may turn into a double retirement as Brock Lesnar could announce his own retirement just after competing with Cena, making it a double retirement.