Roy Rosselló says he’s just glad his honesty could help Erik and Lyle Menendez … admitting he’s glad his testimony wasn’t “in vain.”

The Menudo singer — whose revelation that Erike and Lyle’s father, Jose Menendez, allegedly sexually abused him when he was a kid in the band Menudo — spoke with The U.S. Sun … and, he gave his thoughts on a ruling that prosecutors must show cause why relief shouldn’t be granted to the brothers.

Roy says, “I am proud and happy about the judge’s decision. My testimony was not in vain. To my understanding, these individuals are always innocent victims. Their souls have been lost, condemned, and mutilated, devoid of hope, future, or destiny since the day their father began to abuse them.”

We broke the story … Judge William C. Ryan reviewed two new pieces of evidence — Rosselló’s testimony that Jose abused him in either 1983 or 1984 and a latter from Erik to Andy Cano sent back around the time of the murders detailing his alleged abuse.

Ryan declared prosecutors are “ORDERED TO SHOW CAUSE … why the relief requested should not be granted.” They have a couple more weeks to do so.

A Superior Court judge has already changed Erik and Lyle’s sentence from life without parole to 50 years to life … and, there will be a full parole hearing next month.