Featherweights Gary Russell Jr. and Vasyl Lomachenko will meet for the WBO's vacant belt on a June 21 card at the StubHub Center in Carson, Calif., that also features former welterweight titleholders Robert Guerrero and Devon Alexander in separate bouts against Yoshihiro Kamegai and Jesus Soto Karass, respectively, on Showtime, Golden Boy CEO Richard Schaefer informed RingTV.com on Tuesday.

"We finalized the card, and I don't know the order, exactly, but we're going to have Devon Alexader against Soto Karass in a 147-pound fight, and then we have Russell and Lomachenko, and we have Robert Guerrero against Kamegai. I think that it's one of the most entertaining cards we have ever put together. This is going to be fireworks from the StubHub Center," said Schaefer.

"I think that the StubHub Center is the perfect spot. Somehow, the StubHub Center, it really is the Mecca of boxing in the Western United States, and it always somehow elevates fights, the way that it's built. The fans are virtually almost in the ring, and when you bring entertaining toe-to-toe fights here, the StubHub Center seems to be the best venue in the world for these types of fights. I'll bet that one of those fights is going to be another Fight of The Year Candidate. I don't know which one, because all three of them are great fights."

Guerrero and Alexander are looking to remain in a star-studded group of 147-pounders that includes RING champion Floyd Mayweather Jr., IBF titleholder Shawn Porter, boxer-puncher Keith Thurman Jr., and former titleholder Amir Khan, all of whom have been in action as of late.

"Devon is a big name, Robert is a big name, Kamegai and Soto Karass are two who are good for an upset on any night. They're clearly two of the most exciting fighters in the sport," said Schaefer. "I don't think that you're ever going to see a boring fight from Kamegai or from Soto Karass. So these are four, very exciting 147-pounders, and I could very well see that the winners could fight each other."

The 31-year-old Guerrero (31-2-1, 18 knockouts) even signed with powerful advisor Al Haymon in March, joining a stable that already included Alexander, Porter, Thurman, Khan and Mayweather, the latter of whom unanimously decisioned Guerrero in May of last year, the last time Guerrero was in action.

Guerrero earned a career-high $3 million for his loss to Mayweather, ending his seven-and-a-half-year undefeated streak. Guerrero had won 15 consecutive fights, having previously lost by a split decision to Gamaliel Diaz in December 2005 only to win their rematch with a sixth-round knockout the following June.

A former featherweight and junior lightweight titleholder, Guerrero entered the bout with Mayweather following consecutive unanimous decision victories over Selcuk Aydin in his 147-pound debut in July 2012 and former titleholder Berto in November 2012.

Japan's 31-year-old Kamegai (24-1-1, 21 KOs) will be after his third straight stoppage victory since falling by unanimous decision to Johan Perez last June, and was last in action for last month's fourth-round knockout of Jung-Hoon Yang.

In early January, Guerrero sought separation from Golden Boy, which promotes nearly 100 percent of Haymon's fighters, through arbitration with the California State Athletic Commission. Guerrero did so even as Schaefer insisted that the boxer's contract remained valid and that the CSAC has no jurisdiction to make a ruling because the contract "was not signed under California law" but "under New York law."

In mid-January, the CSAC supported Golden Boy's assertion by declining to hear Guerrero's case and directing the fighter and Golden Boy to resolve their contractual issues in New York.

"I have not sat down with Robert, but I have sat down with Al Haymon, and I said, 'Look, I'd like to have him back and we worked it out,'" said Schaefer. "So he'll be back in the ring on June 21, and hopefully, everybody will putting their best foot forward. Whatever differences there were, they can be put in the past and everybody moves on."

A 25-year-old from Capitol Heights, Md., Russell is 24-0 with 14 knockouts. A 2008 U.S. Olympian, Russell qualified for the team but never competed due to missing the weigh-in. Russell was declared by WBO President Francisco "Paco" Valcarcel in October to be the WBO’s mandatory challenger to face then-beltholder Orlando Salido.

The ruling did not preclude Salido from making a voluntary defense against Lomachenko, which he did on March 1. Lomachenko fell by split decision but Salido lost his belt at the scales after failing to make the 126-pound weight limit.

As a result, the title became vacant.

Lomachenko, 26, had said he had wanted to make history by becoming a titleholder in what was being billed as his second professional fight. According to Fight Fax Inc., Lomachenko is actually 7-1 because he was paid to take part in six World Series of Boxing contests.

"Gary Russell wanted the title shot for a long time, but the fact that word, 'Most Avoided Fighter' is often used in the sport of boxing, but I think that with Gary, that definitely applies, because it has always been very difficult to find opponents who want to fight Gary Russell. Because the fact is that Gary Russell is one of the most talented fighters in the sport, irrespective of weight class, and he's always looking for this opportunity. So he has been waiting for this moment," said Schaefer.

"On June 21, Russell is going to get that opportunity. It's very much Lomachenko's dream as well. Very early on in his career, he wants to become a world champion, so I think that this will be one helluva fight. Two extremely talented amateurs and two of the best amateurs in recent history now competing in the pro ranks with so much at stake. Putting this fight in the middle of those two other fights, you have a helluva card."

The 27-year-old Alexander (25-2, 14 KOs) was dethroned as IBF beltholder by Porter following a unanimous decision in his last fight in Decamber, this, following Alexander's seventh-round stoppage of Lee Purdy in May. Purdy represented Alexanders' fourth straight victory since falling to former WBO 147-pound beltholder Tim Bradley by 10th-round technical decision in January 2011.

Alexander's run had included a split-decision over Lucas Matthysse, who is currently THE RING’s No. 1-rated 140-pounder, as well as a unanimous decision over Marcos Maidana.

Alexander dethroned hard-hitting Randall Bailey for the IBF belt in October 2012 before facing Purdy, and has also knocked out former titleholders Juan Urango and Junior Witter, and decisioned ex-beltholders DeMarcus Corley and Andriy Kotelnik.

A rugged 31-year-old, Soto Karass (28-9-3, 18 KOs) has fought as high as junior middleweight for a fifth-round knockout loss to middleweight title challenger Gabriel Rosado in January 2012, and is 4-2 with two knockouts over the course of his past six fights.

In succession, Soto Karass lost by eighth-round knockout to Maidana in September 2012, scored consecutive wins by unanimous decision over Selcuk Aydin in January 2013 and 12th-round knockout over former titleholder Andre Berto last July, and lost his last fight by ninth-round stoppage to Thurman in December.

Schaefer said that he will confirm the order of the fights with Showtime Sports boss Stephen Espinoza.

"I think that the bout order is going to be opening up with Devon Alexander, and then Russell-Lomachenko fight, and then, you go into the Robert Guerrero fight," said Schaefer. "That's what I am thinking, but I haven't really finalized the bout order yet with Stephen."