Lucius is a just slightly faster, and beats him to the door, blocking his way. "Don't be absurd." he hisses under his breath. "She's the soul of discretion...or she wouldn't be here. Come back in and be a civil adult." He takes a breath, not stupid enough to grab Severus, but with his arm a mere breath away from him. "And I am not using that other name in my own house, you are Severus here, no one else. You tell her to use the other name outside, she will." He watches Severus' face. "I won't apologize for what goes on in my own house, but I did not expect her to come in. But if she heard, it does not matter. She knows who and what I am. We can continue our discussion at any time, but for Circe's sake, come back in."
And Lucius is reacting as calmly as possible. And yes, if Sev can calm down...Lucius had been meaning to tell him about this. No splinching allowed.