The Backstreet Boys have been banned from recording a chat with their incarcerated former manager Lou Pearlman for a new documentary.

The grown-up boy band hope to take fans on a trip through their history in the new film project and they thought an interview with Pearlman, behind bars would be a vital part of their story - but prison bosses ruled they could not take cameras to jail.

Kevin Richardson explains, "For the documentary we reached out to the prison and we were gonna... go in and chat about everything because we talk about him (and) he's obviously a part of our history... but we couldn't get it done. The prison wouldn't allow it."

Pearlman, who discovered the group, was sentenced to serve 25 years behind bars in 2008 after he was convicted of conspiracy and money laundering as part of a long-running Ponzi scheme.

The pop star admits filming the documentary and collating videos and information for the project has been a lot of fun, and he cannot wait for fans to see it.

He adds, "It was like therapy filming it."