That was according to RT himself.. but the previous owner who I bought him from wasn't able to prove it either.. it seems all his offspring were normals.
Well since you dont know if he is het tremper or not you can't/shouldn't breed him to any other strain. I would breed him to a Black Hole het Tremper or a Dreamsickle. This is a fun project (I did it last year but mine was 100% het). You will have a huge array of possible offspring from that pairing.