The surprising detail that kept Princess Diana's original red sheep jumper 'in good condition' after 40 years as it sets to make $89,000

Princess Diana's red sheep jumper is to be sold at auction for up to $89,000 (£70,000) after being kept in 'in good condition' by this surprising detail. 

• The original red sheep jumper worn by Princess Diana will be put up for auction at the end of the summer, more than 40 years after the late royal first donned it. 
• The Warm & Wonderful knit, which had been sent back to the company by Buckingham Palace because it was damaged, was unexpectedly discovered by one of its creators in March. 
• In other royal news, We're obsessed with Kate Middleton's cool £135 white trainers as royal hailed 'model of health and fitness'.
  

The original sheep jumper worn by Princess Diana will be sold at auction next month for an estimated $89,000 (£70,000) after being discovered more than 40 years later in an old wine box. 

The late Princess of Wales was first pictured in the Warm & Wonderful wool garment at a polo match in 1981, shortly before her wedding to Prince Charles. Buckingham Palace had the jumper sent back to the luxury British knitwear label, however, because there was a tear in one of its cuffs. Rather than repair it, Warm & Wonderful decided to send a replacement to Diana and keep the returned one. 

It was unexpectedly discovered by one of the owners of the brand in March, during a rummage around for an old pattern.

"It’s the ultimate Cash in the Attic story, it’s almost corny," Joanna Osborne told the Telegraph, before sharing the secret behind the jumper's lasting high quality. 

"I found an old wine box and it was folded up in there along with a cotton bedspread, which was very fortunate, as it means it has stayed in good condition," she revealed. Cotton allows wool garments to breathe whilst also protecting them from dust and pests, like moths. 

"We didn’t think we had any of the original sheep jumpers because at the time, we were so desperate to complete orders that we never owned one ourselves, so I couldn’t believe I’d found the original Diana sheep jumper," she admitted. "It took a while to sink in. And we’re so lucky it’s not fallen to pieces." 

After realizing the "weight of responsibility" attached to owning such an artifact, Osborne and her Warm & Wonderful co-founder, Sally Muir, decided to contact luxury auctioneers Sotheby's to see if they would be interested in selling the "amazing" sweater. 

Bidding will be open online between August 31 and September 13.