"But the other day she was wearing this lamb foetus coat, made from baby lambs that haven't even been born.
"It's like wet curls. So I said, 'I didn't know you ate foetuses,' and she was like, 'Eeew!' I haven't seen her in it since."
The designer claimed she'd also caught out another pal, actress Gwyneth Paltrow, wearing real fur trim on a jacket.
"I love her, but on the fur thing, people really are very fickle," Stella said.