Last chance for Julio Cesar Chavez Jr. against Marcos Reyes?

After so many unfulfilled promises -- from the positive marijuana test to retiring on his stool – Julio Cesar Chavez Jr. gets one more chance to brand himself as something other than the disappointing son of a legend.

Chavez Jr. (48-2-1, 32 knockouts) will fight Mexico’s Marcos Reyes (33-2, 24 KOs) in the main event of a Showtime/CBS doubleheader from El Paso, Texas, that also includes the U.S. debut of Ireland’s unbeaten light-featherweight world champion Carl Frampton (20-0) as the CBS afternoon headliner.

From the time in 2012 when cameras caught Chavez Jr., 29, eating from a cereal bowl in his boxers as then-trainer Freddie Roach waited for him to prepare for the fight of his life against middleweight champion Sergio Martinez, to the moment in April when Chavez retired on his stool after getting knocked down by Andrzej Fonfara in the ninth round at StubHub Center, malaise, not passion, has defined the boxer.

Now, after the Fonfara loss and splitting with another, Joe Goossen, Chavez has reportedly dedicated himself to maximizing whatever talent he has.

“Junior has expressed more disappointment in himself than anyone else has,” Showtime Vice President Stephen Espinoza said. “That’s the reason he’s fighting again so quickly. He wants to get back in there and set things right.”

Chavez and Reyes, 27, will fight at a 168-pound limit, the figure Chavez couldn’t make two years ago before gaining a highly disputed decision over Brian Vera at StubHub Center.

Now, he’s worked under new trainer Robert Garcia at Garcia’s new secluded Riverside ranch training center.

“All fighters lose, but in this fight Saturday, I’ll never stop fighting,” Chavez Jr. told The Times in a telephone interview. “I’m in better shape. I have more range, more distance … I’ve had a regimented training camp.

“[Garcia] has seen the change.”

Chavez said he’d like to fight at least twice more this year.

“I need to stay busy. Between 2012 and 2015, I only fought three times,” he said, a contract dispute blamed for the layoff. “This is a tough fight, but I know I’m a better fighter now, considering the people I’ve fought.

“At this weight, I’ve never lost. I’m very strong.”

Garcia said he has seen with Chavez moving toward his 30th birthday in seven months a matured person who has taken training camp seriously.

“Things have been easier than I expected. He’s trained hard – two-and-a-half hours every day – he’s full of energy,” Garcia said. “Maybe he had personal problems with others who’ve trained him, but with me it’s like [I’m] an older brother. That’s what he needed. He’s very motivated.

“Being the son of Chavez, he’s maybe never performed the way people expected. Now, he’s comfortable. He looks so much different. I think this training camp was the main reason. I’m not focused on big names with him right now. I just want to keep him busy and show people what I can do with him.”

The El Paso doubleheader will start at noon Pacific time with Riverside heavyweight Chris Arreola (36-4, 31 KOs) fighting Frederic Kassi (18-3, 10 KOs). If Arreola wins, he could earn a third heavyweight title shot, this time against unbeaten Deontay Wilder.

Frampton will fight Mexico’s Alejandro Gonzalez (25-2-1, 15 KOs) in an IBF title bout.

On the Showtime card, which starts at 7 p.m., promoter Don King’s unbeaten junior-welterweight contender Amir Imam (17-0, 14 KOs) opens the broadcast against Fernando Angulo.