Inside the final days of Everest climber Andrew 'Sandy' Irvine

Did they or didn't they? That's the question that has dogged historians and climbing enthusiasts for decades.

Did George Mallory, 38, and Andrew 'Sandy' Irvine, 22, reach the summit of Mount Everest before they perished, or did they die agonisingly close to becoming climbing gods? 

Today, a quarter of a century after Mallory's body was found, it was announced that a team sent by National Geographic magazine discovered what they believe to be Irvine's foot. 

Still encased in a boot and a sock bearing the 22-year-old's name tag, it was found on Everest's Central Rongbuk Glacier, several hundred feet below were Mallory's remains were discovered. 

It has cast new light on mountaineering's greatest mystery. In the years since hat June 1924 expedition ended in tragedy, experts have filled in many of the gaps about what happened to the pair on their final climb. 

The 1924 expedition was the second trip launched with the goal of achieving the first ascent of Everest. 

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Mallory and Irvine's fateful climb came after two unsuccessful attempts on the same expedition. 

The first was made by Mallory and General Charles Bruce, who was initially the expedition leader until he fell ill. 

The second attempt was made by Edward Norton - who took over as expedition leader - and camp medic Dr Howard Somervell. 

For the third attempt, Mallory decided to take Irvine with him, despite his relative inexperience.

Irvine was the group's newcomer, but the former engineering student did have better knowledge of the group's heavy oxygen sets. 

Irvine and Mallory made it up to Camp V - at 25,600feet - successfully and spent the night there on June 6. 

Mallory left a note to expedition geologist that read: 'There is no wind here, and things look hopeful.'

The following day, the pair moved up to the small tent that expedition leader Edward F. Norton established with Dr Howard Somervell - the group's medic at Camp VI (26,800feet).

Here, Mallory sent down via porters two additional notes. 

In one, Mallory told Odell that he and Irvine were 'awfully sorry to leave the camp in such a mess'.

Mallory also complained of the 'bloody load' of the two oxygen cylinders they were each going to carry. He concluded by saying: 'Perfect weather for the job!'

However, the climber, who was known to be forgetful and careless, forgot to pack his hand-wound torch.

He also left behind magnesium flares that would have been useful if the pair were to get into trouble. 

Neither Mallory nor Irvine forgot their long-handled ice axes and strapped on their oxygen sets.

The sets were designed by the Air Ministry back in London. Irvine had modified them so that the bottles were turned upside down, allowing the tube from the valve to the mouthpiece to be shorter - thus saving weight.

Mallory's other note read: 'Dear Noel, We'll probably start early tomorrow (8th) in order to have clear weather.

'It won't be too early to start looking out for us either crossing the rock band under the pyramid or going up the skyline at 8.0 p.m. Yours, G Mallory.

Irvine had mistakenly said 'pm' instead of 'am'. 

The next morning, the pair left their tiny tent after dressing for the day ahead.

They put on woollen trousers, puttees (strips of cashmere wound around the legs), hobnail boots, and Burberry jackets.

The jackets were based on the ones that Ernest Shackleton wore in the Antarctic and were specially made.

Irvine insisted that his jacket have pockets sewn into his jacket. They boasted what were then innovative zip fasteners.

Along with a 9mm white cotton rope, Mallory also had a Kodak camera which Somervell had lent to him. 

In his pockets he had what British mountaineer Graham Hoyland - a cousin of Somervell's - described in his 2013 book Last Hours on Everest as an 'extraordinary collection of junk'.

He had a pair of nail scissors, a pencil, some 'Savoury Meat Lozenges', sun goggles and petroleum jelly. But he had forgotten to take his compass as well.

A mitten found in 2001 suggests that Mallory and Irvine used much the same route as modern climbers.

It could have been dropped on the way up or the way down. 

The pair then left their next clue - an empty oxygen cylinder - 600feet short of what is known as the First Step the first of three rock buttresses. 

Noel Odell wrote in diary that he saw the pair - now two tiny black spots on the rock face - at around 12.50pm. He recalled: 'They were going strong for the top'. 

However, what took place over the next couple of hours is uncertain.

What is known for sure is that a storm started at around 2pm. 

Ice axe evidence suggests that the pair descended the way they had come. 

Mr Hoyland, who organised the 1999 expedition that found Mallory's remains, believes that the older man then slipped and fell.

He wrote: 'Experienced climbers know that the descent is the most common time for this sort of accident to occur; exhaustion and hypothermia are setting in, concentration has been lost as a result of a false sense of security and, because of the slope, you cannot see your next step as clearly as you can on the ascent.'

After Mallory fell, Irvine is believed to have dropped his axe to grab the rope, but was pulled down by his partner's weight.

Mr Hoyland adds: 'I think that they then fell together in the curious, alternating fall that is often the fate of roped men: one falls, pulling off the other.'

Mallory is known to have survived the initial fall because of the fact that severe bruising formed around his waist. 

He is then believed to have staggered on towards Camp VI. His body was found around 900feet away from the camp.  

Irvine's axe was found in 1933. It was identified thanks to the distinctive notches carved into the wood. It was discovered on a tiny ledge below the First Step.

Nothing is known of Irvine's final minutes and seconds, or if he survived his initial fall. 

More details are unlikely to emerge unless the rest of his body is discovered. 

Some experts believe that Irvine and Mallory might have actually achieved their goal before perishing, because they were last seen approximately 800feet from the summit and could have been descending when they fell. 

The camera they were carrying has never been found, but could contain crucial evidence that they reached the summit.

Irvine's remains are now in the possession of the China Tibet Mountaineering Association, the body that issues permits for climbing on Everest's northern side.

The find has been reported to the Royal Geographical Society, the body that organised Mallory and Irvine's original expedition, along with the Alpine Club.

Irvine's family, which includes his great niece and biographer, Julie Summers, has volunteered to compare DNA test results with the remains to confirm they belong to Irvine.