Regulus ignored the Potter boy in favour of Severus. Of course knowing that Potter was here for Severus gave him the perfect excuse to play with him. He went closer and put a hand on Severus' arm. "I promise you that Sirius will be on his best behaviour or you can hex him. I'll help."
He gestured to the door with a hand while the other settled on Severus' back. "Shall we? We'll have to Fire Call before we can go. They seem to have done something right with the security."