He befriended the boy, invited him to stay overnight and told him that demons and spirits would kill him and drag him to hell unless he carried out sex acts.
He dressed in a black cloak and used a crucifix with a skull and crossbones and an onyx ring, which he claimed gave him power, to terrify the youngster into keeping the abuse a secret.
The victim, who is now 32, told how McFadden abused him almost every day for four years, using threats to keep him silent.
This was a fairly monstrous breach of trust. You ran a martial arts club and were well regarded
The victim said: "He started to get us into this black magic. He described himself as a high priest with this black magic circle.
"He said he could have out of body experiences and could talk to demons and spirits.