Regulus/Cassandra
Regulus should have known better than to have a party with James and Sirius. They were unable to do classy, and the Weasley family wasn't much better. Fortunately the house was big enough that most of the fracas was in the pool house.
The adults (and age seemed to have little to do with it) were in the three receptions rooms. He moved around, trying to speak to those who might help with Remus' decision about the cure when he saw the woman that had helped them through the siege.
"Cassandra, if I'm not mistaken," he said, smiling at her. "It's very good to finally meet you in person. I hope you are enjoying yourself."