Perhaps it should be no surprise in the fast and furious mixtape market, but a long-awaited track combining the vocals of Tupac Shakur and 50 Cent has leaked to the streets early, DJ Whoo Kid said Thursday.

"The Realest Killas," a dream collaboration concocted by DJ Whoo Kid and Daz Dillinger, features Snoop Dogg on the intro, telling everyone to say "yes to drugs and f--- the police." Snoop goes on to tell Whoo Kid: "The streets ain't ready for this/ This is heav-eee, maaan/ This is heav-eee!"

Then Tupac's words from Scarface's "Smile" come in, and the slain icon warns, "There's gon' be some stuff you gon' see that's gon' make it hard to smile in the future."

An adamant 50 Cent follows Pac, chastising Ja Rule for shaving his head bald, getting tattooed and wearing bandannas. He claims the Rule's actions mimic Tupac's. "Here's the real Tupac," 50 continues.

Pac's verse is like his vintage street-soldier narratives, and he rhymes such lines as "Since my life is based on sinnin', I'm hell-bound ... / I'd rather be buried than worried," over a drum-and-chime-filled beat that appears tailor-made for a battlefield.

"Till Makaveli returns, it's all eyes on me," 50 sings on the chorus, in a cadence reminiscent of Pac's hook for "All Eyez on Me." "I thought I told you before — don't f--- with me."

50's next verse is dedicated to Ja, as the Southside Queens native again accuses the Hollis, Queens, rapper of being a Tupac wannabe. "You pretended to be Pac, you pretended to be hot," he says.

In New York on Wednesday night, Miami producer Red Spyda, who made the beat for the track, recalled how the song came together. "We was in [the studio] in Miami and 50 was eating chicken. He heard the beat [and] when he heard Tupac's part, he dropped his fork and was like, 'Is the mic on?' and went right in."

Spyda, who also produced the beat for the 50 Cent/Notorious B.I.G. collabo, "The Realest," said that he and Whoo Kid lobbied to get the song officially released but ran up against opposition from Tupac's mother, Afeni Shakur.

"We tried to do a deal, but a lot of politics [got] in the way," Spyda said. "I don't care. It's gonna drop. The streets are gonna be happy, so I'm good."

Donald David, attorney for Afeni Shakur, says that Whoo Kid and company never contacted them about the release of the song. In fact, a cease-and-desist letter was served to Whoo Kid and company recently.   "There may be some flack if that song comes out," David said Friday afternoon, emphasizing that Daz does not have any ownership rights to Tupac's material.   David also stated that the Shakur estate would consider licensing Pac's material to Whoo Kid "under appropriate circumstances."   

Red Spyda, who named himself after his favorite cartoon character, Spider-Man, said the streets are going to stay elated because he plans to release more unreleased verses from B.I.G. and Tupac.

"I have more unheard Biggie songs," said Spyda, who obtains his rare vocals through both legitimate and "sneaky" methods. "I have one with him and Mase nobody has ever heard."

Although he's amped about eventually releasing the Biggie street gems, Spyda said he prefers to leave the cat in the bag about when he plans to do so. "I'mma keep that under wraps," he said. "From what I hear, they're doing a Biggie duets album. I can do something [on] who I think Biggie should do a duet with, [and] throw the record out to get some work. I'd like to see Big with people he rocked with. I don't want to see Big with a bunch of different people. I'd rather throw Lil' Kim or Lil' Cease on there. I won't put Tupac and Biggie on a record."

But Spyda said his upcoming album will feature appearances by both legends as well as other hip-hop trailblazers. Don't expect the project to be sold in stores.

"[This winter] we're going to do a limited-edition mixtape," Spyda said. "All classic rhymes by the illest hip-hop artists ever to touch the ground: Nas, Jay-Z, Big, Pac — the ones everybody knows. I'm gonna build my beats around [the vocals]. It's gonna be a street tape. That's gonna be the next project."

For a feature interview with 50 Cent, check out "50 Cent: Money To Burn."