Welterweight Robert Guerrero's retirement is over.

The former two-division world titlist known as the "Ghost" is ending his retirement and will fight an opponent to be named on the non-televised undercard of the Deontay Wilder-Tyson Fury heavyweight world title fight on Dec. 1 (Showtime PPV) at Staples Center in Los Angeles, the fighter tweeted on Thursday.

I'm here to announce that I'll be fighting on the #WilderFury card as I look to continue my legacy in this sport. #TheGhost is Back! — Robert Guerrero (@GHOSTBOXING) November 8, 2018

Guerrero, who won world titles as a featherweight and junior lightweight, plus interim belts at lightweight and welterweight, has not boxed since suffering the first knockout loss of his career, a third-round stoppage to former lightweight world titlist Omar Figueroa Jr. on July 15, 2017. But Guerrero has been training for the comeback for more than a month, the source said.

Welterweight Robert Guerrero (right) retired two days after he suffered the first knockout loss of his 16-year professional career to former lightweight world titleholder Omar Figueroa Jr. (left) last year. Rich Schultz/Getty Images

A couple of days after the loss to Figueroa, Guerrero (33-6-1, 18 KOs), 35, issued a statement announcing that he was retiring after a 16-year professional career in which he had faced several top names with his bouts being a television fixture.

Guerrero, of Gilroy, California, defeated name opponents such as Joel Casamayor and Andre Berto, but after outpointing Berto in a grueling fight in 2012, he got a chance to fight Floyd Mayweather in a welterweight world title bout that headlined a Showtime PPV card -- the first bout of Mayweather's megadeal with Showtime.

Mayweather trounced Guerrero by lopsided unanimous decision in May 2013, and Guerrero's career went downhill from there. Including the loss to Mayweather, Guerrero went 2-5 before announcing his retirement, suffering losses to top foes Keith Thurman and Danny Garcia as well as journeyman David Peralta and Figueroa.

He did defeat Japanese brawler Yoshihiro Kamegai by decision in a brutal slugfest and got a controversial decision win over journeyman Aaron Martinez.

The fight with Figueroa, which had been Guerrero's first in 11 months, was perhaps the worst of his career. Figueroa, who was coming off his own 19-month layoff, pummeled Guerrero. He knocked Guerrero down five times -- three times in the second round and twice more in the fifth round -- before the bout was stopped.

"A boxer's career is a long and tough road," Guerrero said in the statement last year announcing his retirement. "Many tears were shed, lots of blood and tons of sweat. Many miles were traveled, thousands of rounds sparred. None were easy, and nothing was ever given to me. I earned everything I got the old-fashioned way. I never ducked anyone and fought the best fighters in the world. I fought my way through every obstacle to make sure my fans enjoyed every second of every round of my fights."