Models walk the runway at the Fendi show during Milan Fashion Week Fall/Winter 2017/18. Photo By Antonio De Moraes Barros Filho / Wireimage

The watchword is "authenticity". Fendi's new project is not about a bunch of oldies deciding what's hip: the tips, stories and "looks" featured on "F is for ..." are generated by millennials and passed on to their peers.

"There is nothing that we are selling, we are opening up services for them," Monfardini said, describing rooftop events at the brand's headquarters in Rome where guests get to see emerging artists.

Millennial-loving was in full swing this fashion week, with Gucci giving guests a vinyl record featuring hot US rapper A$AP Rocky, and Dolce&Gabbana using 99 social media stars and cool teens as their runway models.

For its pre-fall 2017 collection Gucci interviewed its models, posting their replies to questions such as "what is your spirit animal" on Instagram.

Brands have been pandering to teenage attention spans and the need for catchy hashtags for social media: Versace and D&G both included hats in their autumn-winter 2017 collections with one-word slogans such as unity, love, power.

Diesel recently hosted an exhibition on "successful living" which featured two-word tips such as "stay sweet" and "be proud".

Gas took the authenticity challenge seriously, shunning stars or their offspring for its summer campaign and instead using students from London's top art and fashion institutes, from the Royal Academy of Arts to Central Saint Martins.