Has to be seen to be believed
Our story starts outside of the Gryffindor common room. Bernie who once guarded this passage herself and was referred to as The Fat Lady has returned to the castle in her new human form to talk to the portrait currently guarding the passage, her old friend Violet.
Violet gasped. "Is that really you, Bern?"
Bernie smiled. "In the flesh."
Violet said, "I had no idea that the rumours about you becoming a human were true."
Bernie asked, "What rumours?"
Violet told her, "That Hufflepuff student you often talked about, Macduff or whatever his name is has been saying such stories about how he managed to find a spell to turn a potion into a drawing which turned you human and, well, here you are."
Bernie chuckled. "Macmillan, his name is Ernie Macmillan."
Violet replied, "Yes, him."
Bernie beamed, "Well, the rumours are true because he did do that."
Violet muttered, "How is this even possible?"
Bernie responded, "Trust me, Vi, the specifics are far too complicated to explain to you."
Violet sighed. "I thought that we were best friends, Bern..."
Bernie rolled her eyes. "Oh, very well, but I will only stay until a student needs in or out."
Violet grinned. "Deal."