Myer milliner Natalie Bikicki wasn't always in the business of making expensive hats; by her own admission, "I'm pretty sure I've already made the world's cheapest hat!"

How times have changed. Come Derby Day, in the Myer marquee, model Kate Peck will be debuting Bikicki's collaboration with jeweller John Calleija, a headpiece that has been billed "the world's most expensive hat."

It ought to be: attached to the laser-cut leather and latex black crown are 1264 diamonds, putting the final pricetag at $3 million.

Making it was a challenge. On Bikicki's side, "I made sure there's a lot of padding. It is heavy – there's no way around that – with 200 grams of weight just from diamonds at the front. I wanted to make sure the wearer didn't need two Panadols at the end of the day."

There was also the matter of materials used. "I don't think leather and latex would have been the first choice for other designers. I wanted something that was really young and subversive, that you wouldn't normally expect from a luxury piece."

That it is. The crown consists of ropy horns, weaving their way around the head, with an enormous Green Beryl jewel at its centre.

Early on, Bikicki found great support in John Calleija, a jeweller with stores in Sydney, the Gold Coast and London. He was immediately intrigued saying, "When the opportunity comes up to make something avant-garde and let your creative spirit run free, I couldn't miss it."

Apparently so, since this is not his first eccentric piece.

"A commercial fisherman in Europe asked us to create a fully encrusted diamond prawn-brooch, but after I gave him a quote, we didn't end up doing it. I joked that it was too much per kilo."

He did, however, create the world's most expensive champagne glasses, clocking in at half a million for the pair. "They came with a warning – not dishwasher safe!"

This time, he was mindful of creating a piece that was beautiful.

"You've got to be careful you don't make it look kitsch," says Calleija.

The result is something that Bikicki hopes is a nod to the mythology that inspired it "rather than something along the lines of Fifty Shades of Grey. I like allegory and I was reading about Diana, Goddess of the Hunt. This is a strong woman who's independent – if she's going to wear an adornment, it would be horns, something animal-like. With a girl like Kate [Peck], you're marrying two ideas: it's both modern and very earthy."

After the racing carnival, the hat can be separated into three pieces – to be worn as a brooch or necklace, for instance – potentially to be sold individually.

But on Derby Day, model Peck will wear it as it was intended, with a security guard in tow.  Is there a danger of the jewels coming loose? "Only the ones I try to swallow on the way out," jokes Bikicki.