One of the most famous garments of the 20th century is about to hit the auction block — and it's touring the world first. Princess Diana's black off-the-shoulder Christina Stambolian gown, better known as the 'revenge dress', goes under the hammer at Sotheby's in New York this December, with an estimate of $150,000 to $300,000.

The dress earned its nickname on 29 June 1994, when Diana wore it to a Vanity Fair party at London's Serpentine Gallery. That same evening, a televised interview aired in which the then Prince Charles acknowledged infidelity during their marriage. Diana, advised by stylist Anna Harvey to simply look 'a million dollars', stepped out in the daring, shoulder-baring look that broke from royal convention — and made fashion history.

She never wore it again. Instead, in June 1997, she included it in a charity auction of 78 pieces from her wardrobe, a sale Prince William reportedly suggested, raising money for causes including cancer and AIDS charities. The dress has stayed with a private collector since — but now that chapter is closing. The consigner, whose late husband won the original bid, says she hopes it goes to someone who will enjoy it as much as they did. A portion of the new sale's proceeds will go to NHS Lothian Charity on behalf of the Royal Edinburgh Hospital, and the lot comes with a rare auction catalog signed and numbered by both Diana and Stambolian.

For anyone hoping to see it in person before it disappears into private hands again, the dress has a busy public schedule. It first goes on show at Sotheby's London from 18 to 24 September, timed to London Fashion Week, then travels to Hong Kong and Geneva. Its final public stop is Sotheby's Breuer Building in New York, where it will be displayed from 2 December ahead of the live auction on 9 December.

Sotheby's Morgane Halimi puts its appeal neatly: what made the dress extraordinary wasn't just who wore it, but what it communicated — one of the most powerful messages Diana ever sent, on her own terms, during one of the most scrutinised moments of her life.

Even if bidding isn't in your budget, the free exhibitions in London and New York are a rare chance to see a piece of royal history up close — and a good excuse to build a fashion-flavoured trip around either city.