During the 1924 expedition, Mallory and his climbing partner, Andrew Sandy Irvine, disappeared on the north-east ridge of the Everest. The pair were last seen when they were about 800 vertical ft (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 had reached the summit before they died remains a subject of speculation and continuing research.