Regulus was an animagi. It wasn't a widely known fact. Initially, he did because he found out Sirius was one too. It was a nice secret between the two of them. Something that kept their bond alive even when they weren't speaking or living together.

Then you came along, and Regulus told you after a while. It was his version of commitment and promise. Now you knew that Regulus was a silly black cat when the world got too tiring.

Tonight was one of those evenings. A small cat meowed as he pushed the door open and walked into your dorm. He jumped onto your bed and nuzzled between your chest and the book in your hands.