During the 1924 expedition, Mallory and his climbing partner, Andrew "Sandy" Irvine, disappeared on the northeast ridge of Everest. The pair was last seen when they were about 800 vertical feet (245 m) from the summit. Mallory's ultimate fate was unknown for 75 years, until his body was discovered on 1 May 1999 by an expedition that had set out to search for the climbers' remains. Whether Mallory and Irvine reached the summit before they died remains a subject of speculation and continuing research.