WWE U.S. Champion John Cena is set to take some time off at the last quarter of the year to begin the filming of a fitness-themed reality show on FOX, per Scott Keith of Blog of Doom. Cena is not scheduled for any WWE show until the company's post-Christmas tour, as reported by Wrestling Inc.

With this news, the 15-time WWE World Champion has to drop his U.S. title, and the rumors began to swirl on who will dethrone him. It was announced that he will hold his U.S. Open Challenge at Hell in Cell, per WWE.com.

At Hell in a Cell live on WWE Network, Cena opened the show and waited for his opponent. Zeb Colter made his return in a scooter and introduced the challenger, none other than former WWE World Champion Alberto Del Rio.

Del Rio was welcomed by the Los Angeles crowd with a big pop as he went back and forth with Cena. He was able to counter the Attitude Adjustment into a backstabber before delivering a huge super kick to Cena's face, winning his first U.S. championship, per WWE.com.

The report noted that the Mexican superstar became the 18th foreign-born U.S. Champion in WWE history, ending Cena's second shortest reign as U.S. Champion in just 34 days. This was Zeb Colter's first appearance since December of last year when he was attacked by Rusev backstage as a part of his feud with Jack Swagger, with Lords of Pain initially reporting that WWE has no plans for the character and won't be brought back on television.

It is an unlikely pairing as Del Rio once feuded with Jack Swagger, with Colter as his manager. They squared off for the World Heavyweight Championship last 2013 with Alberto retaining his title at WrestleMania 29 via submission.

The match against Cena was the 38-year-old Mexican's first match with the WWE since being fired last August 2014. He was fired for unprofessional conduct. He reportedly slapped an employee who allegedly made a racist joke towards him, per WWE.com.

He spent most of his time last year with AAA in Mexico and El Rey Network's Lucha Underground. According to PW Insider Elite via Wrestling Inc, there were a lot of backstage talks in recent weeks about the possibility of bringing Del Rio back to become WWE's top Hispanic star.

In a recent interview with Raj Giri of Wrestling Inc, Del Rio revealed that he was on good terms with WWE after he was fired. "Oh, we're good. We shook hands, we talked about what happened. They apologized, I apologized. We're good right now. I'm pretty happy with what I'm doing now," he said.