John Cena was suddenly a part of an unexpected match tonight on WWE SmackDown. Unfortunately, there was a disaster waiting for him.John Cena was interrupted by Sami Zayn tonight, as the latter came out and thanked Cena for all that he had done for him over the years. He went on to say that Cena had inspired him and given him a title match; now, he wanted to return the favor, giving him the chance to wrestle for the United States Championship.Sami Zayn also announced the return of the regular title matches for the US Title, dubbing it the Sami Zayn United States Open Challenge.Cena and Zayn squared off in the ring in what will be a last-time-ever match between the two stars as the legend is set to retire in a few months. The match saw Cena use the Angle Slam and the Angle Lock, looking to pay respect to the Hall of Famer. The Pop-Up Powerbomb was also used, paying tribute to Kevin Owens.Zayn came back and hit the AA himself, getting a near-fall. Cena returned the favor with an AA of his own for a near-fall. There were Helluva Kicks, a GTS, a Spear, all delivered, and it looked like it was over after the star hit an Avalanche AA from the top rope. However, the match finally came to an end thanks to Brock Lesnar. The star made his way out to the ring, pulled the referee out, threw Sami Zayn out with an F5, and then hit John Cena with repeated F5s as well, before finally leaving.John Cena Has a Huge Challenge Ahead of Him in the Form of Brock LesnarAt SummerSlam, Brock Lesnar returned to suddenly attack Cena and destroy the star completely. Coming after his loss to Cody Rhodes for the WWE title, it was expected that it would be his next feud, but instead, the star went on to battle Logan Paul at Paris.With Lesnar disappearing, there was little that anyone could say about what was next. Now, the star is back. It is expected that the two stars will face each other at WrestlePalooza.