The bombshell sex-trafficking case against Sean “Diddy” Combs turned out to be the “most expensive prostitution trial in American history,” one legal expert told The Post.

Defence attorney and former prosecutor Neama Rahmani offered up the glaring assessment before Combs was acquitted Wednesday on federal charges of forcing his former lovers to live out his degrading sexual fantasies, but was found guilty of lesser prostitution charges.

“Like I’ve said all along, this case will come down to racketeering,” Rahmani said as jurors were still weighing the case against the disgraced hip-hop mogul.  

“If the government doesn’t get a RICO conviction, this will be a huge loss and the most expensive prostitution trial in American history.”

Rahmani had speculated that if the feds ultimately didn’t secure a guilty verdict on the racketeering count, the case would really only boil down to two prostitution charges.

The lawyer said sex trafficking would be difficult to prove because “consent is a defense” and Combs’ lawyers had shown a plethora of text messages that his accusers were eager to participate in “freak-offs” — sex marathons with male prostitutes.

He predicted, too, the outcome of the jury’s verdict.

“What a tremendous loss for the prosecution. And a huge win for the defense,” Rahmani said just moments after the verdict was handed down.

The Bad Boy Records founder was ultimately found guilty of two counts of transportation to engage in prostitution and was acquitted on two sex-trafficking charges and one racketeering charge.

The mixed result, which came on the third day of deliberations, capped a two-month trial that revealed twisted details about the mogul, including his insatiable taste for the “freak-offs.”

The acquittals on the sex trafficking counts mean he will avoid a 15-year mandatory minimum sentence.

Combs now faces a maximum 10-year prison sentence on each of the two prostitution counts.

The judge will determine Combs’ sentence at a later date and will decide later Wednesday whether he can walk free until then.