It came with a blank wedding invitation printed on royal stationery.
Julien's executive director Martin Nolan said the auction house sold a piece of cake from the wedding of Princess Diana and Prince Charles a few years ago, which brought around US$6000.
The cake was 27 years old at the time.
This auction included bidding on other royal items as well, as five of Princess Diana's dresses were set to be auctioned off. The dresses are expected to fetch US$60,000 to US$100,000 each.
Catherine and William's cake was a bespoke creation, crafted by cake-maker Fiona Cairns. It took her five weeks to complete the confectionery masterpiece.
The elaborate gateau was covered in cream and white icing and decorated with 900 delicate sugar-paste flowers. The culinary masterpiece took center stage at the Buckingham Palace reception held in the picture gallery on the day of their wedding.
Ms Cairns, 59, whose confections are sold in Harrods, Selfridges and Waitrose, was contacted by St James's Palace in February and asked if she would make William and Kate's wedding cake.
It appears that the humble slice of wedding cake may be worth its grand price tag as Ms Cairns says that creating the dessert was a meticulous and exhausting task.
"We reflected some of the architectural details in the room so the garlands on the walls were reproduced loosely on the fourth tier - we've used roses, acorns, ivy leaves, apple blossom and bridal rose."
The bride wanted elements from the Joseph Lambeth technique of cake decoration, where intricate piping is used to make three dimensional scroll work, leaves, and flowers.
Catherine also gave Ms Cairns detailed instructions for her to include 17 different blooms and foliage for their meaning or symbolism - known as the "language of flowers".
Also under the hammer is a blank invitation to the same wedding, printed on Queen Elizabeth II's Buckingham Palace stationary.
"The Lord Chamberlain is commanded by The Queen to invite _____ to the Marriage of His Royal Highness Prince William of Wales, K.G. with Miss Catherine Middleton at Westminster Abbey on Friday 29th April at 11.00 a.m.," it reads. "Dress: Uniform, Morning Coat or Lounge Suit."
- Daily Mail