Regulus was mostly pretty sure that Cassi meant it about just the three of them, but he'd definitely been burned in the past in the area of surprise parties. Therefore, he arrived at his sister's house a bit warily, half-expecting a horde of people he barely knew to leap out at him, and relaxed rather noticeably when the place seemed to be empty.
"Hello, Cassi," he greeted her, giving her a hug and a quick kiss on the cheek. "Thank you for doing this, I really do appreciate it."