The former child star appeared on "The Today Show" Monday, where he opened up about the trauma he faced at the hands of former dialogue coach Brian Peck ... confirming BP owned a signed painting of serial killer John Wayne Gacy.

Drake says ... "[T]hings were happening to me in a room where there’s a painting by one of the most prolific serial killers who preyed on young boys staring at me. So, now that puts in my mind, 'How far is this really gonna go?'" Gacy killed 33 young men and boys in the '70s.

Gacy also infamously raped and tortured many of his victims -- stashing their bodies under the floorboards of his home ... which is why Drake's confession is extra disturbing.

The fact Peck had a JWG painting at his home was actually touched on in the 'Quiet on Set' documentary -- and other Nickelodeon stars at the time also found it strange and off-putting.

As you know, Peck -- who worked closely with Drake during his tenure at Nickelodeon and a slew of other children's shows -- was sentenced to 16 months in prison and had to register as a sex offender for abusing DB as a teen.

However, it wasn't until the 'Quiet on Set' docuseries where it was revealed that Drake was Brian's victim ... during which DB detailed how he was groomed and manipulated by Peck.

On top of this troubling thought Drake had -- he got emotional musing on what he would tell his younger self if he could go back and talk to him ... choking up and fighting back tears as he noted there wouldn't be much he could say other than to get ready.

Drake also said in his interview that he told his story, in part, because of his son -- and wanting to be honest with him, while letting him know he's been through the fire and back.