Complex sentence: It first appeared in a short story by J.K. Rowling on Pottermore on June 28,2016, and its first onscreen mention was in "Fantastic Beasts and Where to Find Them".
Split into simpler sentences: It first appeared in a short story by J.K. Rowling on Pottermore on June 28,2016. Its first onscreen mention was in "Fantastic Beasts and Where to Find Them".