The Duchess of Cambridge's wedding dress cost £250,000 and was kept a secret even from the dressmakers.
It has been revealed that it took 20 embroiderers four weeks to sew the intricate lace details.
However, they had no idea it was for the royal bride and did not know it was designed by Alexander McQueen protégé Sarah Burton.
The team of workers from the Royal School of Needlework (RSN) were told the gown was being made for a TV period drama.
A source told the News of the World: "This was the most expensive and secretive project we've ever been involved in. Nobody had any inkling it was for the royal wedding."
The seamstresses, who ranged in age from 19 to 70, replaced their needles every three hours to keep them sharp and clean.
Based at Hampton Court Palace, the team also had to wash their hands every 30 minutes to make sure the lace stayed spotless.
The ladies only found out the dress was for Kate two weeks before the wedding and were sworn to secrecy.
The source said: "We were assured money was no object because it was being made for a period television drama - which is a good job, because it came in at about £250,000.
"We were astonished when we found out the truth. We were just so proud to have been involved with such an amazing spectacle."
Burton said: "I am delighted that it represents the best of British craftsmanship."
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