Kate Middleton wore a pair of knee-high hiking boots for a six-hour trek to the Tiger’s Nest monastery on her visit to Bhutan in April. The Duchess of Cambridge has been sporting these boots since over 10 years and finds them very reliable. The designer behind Kate’s hardy and long tassel boots, Penelope Chilvers spilled some secrets about the making of the footwear.

The Penelope Chilvers long tassel boots are priced at 475 pounds ($697). The 34-year-old royal paired her brown colored boots with dark skinny jeans, a white shirt and leather gilet. Kate looked practical in the outfit for the long and tough trek, however, she did not wear the hiking boot she has packed for the tour.

Kate Middleton wears long tassel boots by Penelope Chilvers Britain's Prince William, Duke of Cambridge and his wife Catherin Duchess of Cambridge, trek up the mountain to the Paro Taktsang Monastery, Bhutan, April 15, 2016. Photo: PHOTO: REUTERS/CATHAL MCNAUGHTON

The flat boots which are a style essential has been inspired by and designed for travel, adventure and exploring. “I make footwear for adventure. It’s not for putting in a wardrobe and keeping in a shoe bag,” said the London-based designer.

She said it is a kind of footwear which can be worn anywhere and the wearer could do anything wearing them. Penelope established her business from a small kitchen table in 2005. She added that she loved to travel to new countries and pick up pieces of leather work.

The designer explained in a short film about her ideas and inspiration. She said she loved the hunt and chase in her job of finding what she is looking for. Her ideas maybe small in the beginning but later turns out into something big or a complete collection, Penelope added.

The designer’s hunt for something also ends up into a new product, but she told that she did not know what she was looking for, until she found it. Her other source of inspiration is the equestrian aesthetic. She said that looked at saddles and bridles, to understand how they are made, where their studs are, where they are stiches and how they are put together, and then finally put into her footwear.

Penelope’s boots are handcrafted in Spain at family run factories, using only the best quality leather. For her footwear is all about “form and function.” Besides, the designer believed in beautiful footwear, with no corners cut and functionality.

The designer works with her friend and pattern cutter Jose Maria who she cannot do without. Her footwear leather is sourced locally in Spain and is dyed with vegetable dyes. Penelope’s celeb clients include Claudia Schiffer, Alexa Chung, Keira Knightley, and Cate Blanchett, apart from Kate.

Kate was first pictured in the long tassel boots at the Game Fair at Blenheim Palace in August 2004. She then wore the same pair a year later at the Gatcombe Festival of Eventing in Gloucestershire.