Islamist fanatics, as you would expect, are very earnest about their beliefs. They accept that secrecy and deceit are necessary to mislead the enemy, but they do not expect their leaders to be lying to them. When they find out that they have been lied to, consistently and over a long period of time, they get very cross—and this has repercussions in the real world.

From the time that the Taliban conquered Kabul and took over most of Afghanistan in 1996, Mullah Muhammad Omar Mansoor was the man who ran the show and was effectively the head of state. He was the man who allowed Osama bin Laden to set up camp in Afghanistan. And although the Taliban lost power after the U.S. invasion in 2001, Mullah Omar remained in control of the organization until his death in 2013.

The trouble is that nobody told his faithful followers that he died more than two years ago in Pakistan. Until last week the Taliban was still issuing statements in his name—most recently, on July 15, a message endorsing the Taliban’s recent peace talks with the current Afghan government. Now all Mullah Omar’s statements since April 2013 are in question, and so are the men who made them in his name.

This matters a lot, because Mullah Omar was not just the leader of the Taliban. He was also the most important figure in the broader alliance of Islamist groups known as al Qaeda. Indeed, he had as much right to claim to be its founder as the man who actually gets the credit, Osama bin Laden.

With his long record as a real fighter, Mullah Omar was much more respected than the man who formally inherited al Qaeda’s leadership after Osama bin Laden was killed in 2011, the reclusive Egyptian theorist Ayman al Zawahiri. Indeed, Zawahiri felt compelled to renew his pledge of allegiance ("baya") to Mullah Omar when the rival jihadi group, Islamic State, declared its leader, Abu Bakr al Baghdadi, to be the "caliph of all the Muslims" in 2014.

This is not just internal politics in a local jihadi group. Al Qaeda and Islamic State are in a frequently violent competition for the loyalty of all the scattered Islamist groups in the Muslim countries. It was therefore very important for al Qaeda that Mullah Omar rejected Baghdadi’s claim to be the caliph—and it is very important to the rest of the world that the two jihadi organisations remain divided and hostile to each other.

Al Qaeda has been losing ground in this competition for some years now. Indeed, Islamic State recently set up its own rival franchises in the two countries where al Qaeda still dominates the struggle against the local regime, Afghanistan and Yemen. The two groups are currently at war with each other in both countries, but that could change fast if al Qaeda’s leadership is discredited by the lies it has been telling.

If Mullah Omar actually died in 2013, he could not have denounced Baghdadi’s claim to be the legitimate caliph in 2014. Similarly, Zawahiri’s pledge of allegiance to him in 2014 was either a deliberate lie, or a demonstration that he is hopelessly out of touch with what is actually happening beyond his hideout, presumably somewhere in Pakistan. Either way, al Qaeda loses credibility.

So do the Taliban, of course. When the self-declared new leader of the Taliban, Mullah Muhammad Akhtar Mansoor, acknowledged that Mullah Omar is dead at the beginning of this month, he carefully omitted any reference to when Omar died. But the Taliban fighting groups are in chaos, because Akhtar Mansoor, then officially Omar’s deputy, issued statements in Omar’s name condemning Islamic State as recently as last month.

Many Taliban groups are now questioning Akhtar Mansoor’s claim to the leadership. His response has been to break off peace talks with the Afghan government and launch some particularly vicious attacks against the Afghan police and army, but it may not be enough to secure his position. As for Ayman al Zawahiri, he hasn’t been heard from since last September.

There would be no reason to mourn the decline of al Qaeda except that the main beneficiary will be Islamic State. There is no strong reason to prefer one organization to the other, either—except that the last thing the world needs is for Islamic State to take over all of al Qaeda’s franchises and create a single, much more powerful and attractive Islamist fighting front.

The current state of division of the extreme Islamist movement is deplored by almost everybody in both organizations. There is little ideological difference between them, although Islamic State is more apocalytic in its vision. If al Qaeda’s claim to leadership is seriously undermined by its lies about Mullah Omar, the unification of most or all the Islamist groups under Baghdadi’s authority is a real possibility.

The first victim of that would be the Assad regime in Syria, which is already tottering, and an Islamist takeover of the whole country. But much more might follow, and none of it would be good news.