Kate Middleton got Prince William's attention by wearing a $40 see-through skirt as a dress at a college fashion show

• Kate Middleton turned a see-through skirt into a dress for a college fashion show.
• The bold outfit is what sparked Prince William's interest, according to a new ITV documentary.
• The couple met at the University of St. Andrews in the early 2000s.

Kate Middleton wore a $40 sheer skirt as a dress during her student days, which is reportedly what sparked Prince William's interest.

The Duchess of Cambridge wore the dress at a fashion show at the University of St. Andrews in 2002, which was attended by the prince.

The Duke and Duchess of Cambridge met at the Scottish university and were friends for more than a year before a romantic relationship developed, William once told The Telegraph.

It was Middleton's bold appearance at the fashion show that changed things between them, according to a new documentary, "The Day Will and Kate Got Married," which aired on the UK's ITV on Wednesday.

Middleton decided to turn the skirt into a dress at the last minute, the documentary reports.

"A switch had been flicked, he suddenly saw her in a different light, and I really believe that was the turning point in their relationship," Katie Nicholl, royal correspondent at Vanity Fair, said in the documentary.

The dress was designed by Charlotte Todd and cost approximately $40 to make, E! News reports.

Todd previously told People that she designed the dress as part of a university project, titled "The Art of Seduction."

"I didn't know who Kate Middleton was and I didn't put her in it. It was just pure chance," Todd told the publication.

William's friend Pat Duncan, who attended the fashion show, said he witnessed William's reaction first-hand.

"She was in a very daring dress, in a sheer, stocking-like dress," Duncan told E! News in 2011. "He was sitting front row and his eyes were like stalks."

The prince told Middleton "she was a knockout" and leaned in for a kiss at the afterparty, a source who reportedly attended the party told Nicholl.

"At one point when William seemed to lean in to kiss her, she pulled away. She didn't want to give off the wrong impression or make it too easy on Will," the source told Nicholl, E! News reports.

The dress was sold for $125,000 at a charity auction weeks before Middleton and William's royal wedding in 2011, InStyle reported at the time.

Charlotte Todd did not immediately respond to Insider's request for comment.