The collection includes a cut-price version of the sapphire blue silk Issa dress Kate wore to announce her engagement to Prince William – the dress that put the London-based label on the map.
Made from jersey, the dress is strikingly similar to style and is described as a "daywear" version of the dress that comes in at £65 – just a snip of the £565 price tag of the original.
The dress is bound to be an instant sell out when the collection is available on 8 August – after Kate's appearance wearing it, it was subsequently reproduced in the same shade and went on to sell out again and again on net-a-porter and in Harvey Nichols.
It is good timing for the fashion retailers, who have unveiled their collection just one week after Kate gave birth to Prince George.
The Duchess of Cambridge is also a fan of Banana Republic – she is said to have bought several items from their summer collection for her honeymoon in 2011.
The US-based brand, known as the grown-up sister of Gap, its parent company, offer the simple, elegant pieces favoured by Kate.
The collaboration offers printed wrap dresses, tops and cardigans ranging from £45 to £85. Accessories range from £29.50 to £99.50 for a tote bag.
Issa was founded by Brazilian-born Daniella Helayel in 2006, but she announced that she was parting ways with the brand by mutual agreements in May this year.
"The time has come for me to move on to focus on my art, travel and other interests," she said in a statement.
In 2011, Camilla Al Fayed, daughter of former Harrods owner Mohammed Al Fayed, bought a majority stake in the company in a bid to enable global growth. She remains the majority shareholder.
The collaboration was announced back in April. Speaking about the project, Banana Republic's creative director Simon Keen said, "We always love animal prints such as zebra and giraffe stripes.
"Issa took that and modernised it. I love that the collection is our world and their world."