"The company bought less product because we wanted the line to be that much more exclusive, so these are all truly limited Roberto Cavalli items," said an H&M spokesperson at the Knightsbridge store.

In Milan, the reception was equally enthusiastic.

"In the beginning, I wasn't sure about the quality but now that I have them in my hands the silk dresses are amazing," said Vanessa Casali, who was laden with animal-print items.

"Where else can you find a fur jacket like this one?" asked Rosi Novara, a lawyer.

Alfio Camuglio, an H&M visual merchandiser, said the fake fur jackets, silk leopard dresses and trenches sold fast.

"I am a huge fan of Mr. Cavalli," said Michela Argelati, holding pretty much every piece of the collection. "Today is a fairy-tale moment and I am the princess with a new wardrobe to purchase."

Patrizia Ferro, a student, said she studied the H&M designer collaborations in college and was curious to see one. "Now that I am here, I can't resist shopping," she added.

A crowd of about 50 formed outside of Berlin's biggest H&M store in the new shopping center on Alexanderplatz. Once the doors opened, chaos ensued as customers moved quickly from rack to rack, frantic to claim their sizes and head to the fitting rooms. In the first half hour H&M employees rushed to restock and lines formed for the fitting rooms and at the cash registers. Though the prices were more expensive than traditional H&M prices, customers showed no hesitation when it came time to pay. Leaving the store 10 minutes after it opened, a customer weighed down with three bags said she was pleased with the prices, "For Cavalli, they were totally OK!"

Cavalli, however, wasn't interested in introducing his own lower-priced line. "My fashion is made in Florence," he explained. "H&M did a very good job. For sure [the clothes] don't have my details. Absolutely not. I leave to them [H&M] to do what they do best."

— With contributions from Samantha Conti, London; Chiara Hughes, Milan; Rachel Brown, Los Angeles and Sarah Rienhoff, Berlin