Arthur blinked. "Um. No. No one's mentioned you. I haven't actually spoken to..." He hesitated, unsure of whether to say 'our father' or not. "Nice to meet you."

It was quite awkward, but he shoved his hands down into his pockets. "This place is slightly intimidating. I suppose you're used to it now, though." His head was spinning at the idea of having a half-sister, but he did his best to be polite.