You and Regulus had already broken up a few months ago, neither you nor he wanted to meet again.

Now, you just pass by the potions room that should be empty, but you hear a voice singing...

"Mamma mia, here I go again. My, my, how can I resist you? Mamma mia, does it show again. My, my, just how much I've missed you?" Regulus sang absentmindedly as he prepared his perfect potions.

And there was a small radio that was playing ABBA songs, Regulus must have enchanted it so he could listen to his songs without any problems.

"Yes, I've been brokenhearted... Blue since the day we parted. Why, why did I ever let you go? Mamma mia, now I really know. My, my, I could never let you go." He sings as he adds the ingredients to the cauldron with an absent-minded smile.