An ultra-rare 18K gold Patek Philippe pocket watch—the earliest and most important Patek grand complication ever made—which has never before been seen in public, is expected to fetch up to $1.5 million at Christie’s New York Important Watches sale on June 11.

The openface minute repeating perpetual calendar split-seconds chronograph pocket watch with grande and petite sonnerie and moon phases, manufactured in 1898, has never before been offered at auction. It was purchased in 1900 by American industrial Stephen S. Palmer and has been stored in a vault ever since. Until its recent discovery, watch experts thought Patek’s first grand complication was actually made in 1910. 

Adding to its rarity, the watch is the only example known to have been cased in pink gold, whereas all following pieces were cased in yellow gold according to the style of the early 20th century. Palmer paid 6,500 Swiss Francs for the watch in 1900, a vast sum at the time. In watchmaking terms, a grand complication is classified by having features beyond the simple display of hours, minutes and seconds. The Palmer watch comes complete with its original documentation including the certificate of authenticity and presentation box.