BIOGRAPHY - Page 16
Not long thereafter, the Illuminati were reassembled by one outside their number: T'Challa, the Black Panther. Although he rejected the idea of the Illuminati at the beginning, T'Challa found himself desperate for allies in a new threat. A woman calling herself a Black Swan fell to Earth from a second Earth hovering in the skies over Wakanda, then used a device to destroy the Earth she came from. She brought with her a tale of Incursions, inter-dimensional events where two Earths crossed into each other's space. Once they did, the Earths either annihilated each other and their respective universes, or one Earth was destroyed, saving both universes. 
T'Challa summoned the Illuminati to brainstorm this multiversal threat, even Namor, who was still considered a war criminal in Wakanda. While they met in secret in the Wakandan Necropolis that T'Challa ruled as King of the Dead, the Panther made it clear he still planned to kill Namor for his crimes against Atlantis once the situation resolved itself. [New Avengers (3rd series) #1-2]
The Illuminati planned to confront the next Incursion with the fully assembled power of the Infinity Gauntlet. They recruited Hank McCoy, the Beast, as heir to the recently-deceased Charles Xavier's Mind Gem in order to gather all the Gems. When the Infinity Gauntlet was formed, Captain America used it to force back the invading Earth, ending the Incursion without either world being destroyed. Unfortunately, something went wrong with the Gauntlet and the Gems were shattered or lost as the Incursion ended. Namor lost his cool and actually struck Cap in anger for "misusing" the Gems. In the aftermath, Namor and the Illuminati sided against Captain America, who took an inflexible moral stance opposed to making plans to destroy inhabited Earths to save their own during the coming Incursions. Doctor Strange cast a memory spell on Cap, expelling him from the group with no recollection of the Incursions, as the Illuminati moved forward without him. [New Avengers (3rd series) #3]
Namor was by far the most vocally negative of the Illuminati, openly mocking his fellows who remaining optimistic about their chances of success, or of holding on to their personal morality in the face of such a threat. Still, merciful fate allowed the Illuminati to keep their scruples intact through several following Incursions. The next foreign Earth was in the process of being devoured by an alternate Galaktus when the Incursion took place. The Illuminati vainly struggled to stop Galaktus's feeding before retreating to their universe with his Herald, Terrax the Truly Enlightened, as a captive. The next Incursion uncomfortably took place in Doctor Doom's Latveria, but it involved a devastated world of the Sidera Maris, the Mapmakers, and therefore contained no life to preserve. It was the Black Panther who first destroyed a world for the Illuminati, using the trigger for their anti-matter bomb to obliterate the Mapmaker world. [New Avengers (3rd series) #4-6]
Despite the enormous scale of the Illuminati's work, the regular world continued spinning, and relations between Atlantis and Wakanda deteriorated rapidly. As the nations inched towards outright war, Namor approached T'Challa in the Necropolis to sue for peace. As was his way, Namor did so arrogantly by stating he was doing Wakanda a favor by offering them a way to avoid war, but he correctly assessed the situation with the Incursions as more important, and the nations could not afford distractions at this time. Unfortunately, the situation was complicated by the fact that T'Challa no longer sat on the throne of Wakanda. He merely served as King of the Dead, while his relatively-untried younger sister Shuri ruled as queen. T'Challa agreed to support Namor's peace request, but when it came before the war council, T'Challa's support failed and Shuri pushed for war against Atlantis. [New Avengers (3rd series) #7]
T'Challa spoke to Namor in the Necropolis to inform him he was being lied to by the Wakandan delegates who agreed to consider peace. When Namor realized the attack and betrayal T'Challa was talking about was happening as they spoke, he raced back to Atlantis, but arrived too late. 
The Wakandan military had devastated his people in a bloodbath that left the Atlantean army in disarray and the people crying in the ruins. [New Avengers (3rd series) #8] It was at this point Proxima Midnight arrived in Atlantis on behalf of Thanos' Black Order. The Mad Titan sought the missing Infinity Gems, and his spies tracked the Gems to the Illuminati. Unprepared to provide even a token resistance, Namor surrendered Atlantis to Thanos' general in exchange for his people's lives. Out of spite for his tragedy, Namor lied and pointed the Black Order at Wakanda, claiming the Black Panther held the Gem they were looking for. The Golden City of Wakanda suffered great losses as a result of Namor's misdirection. [New Avengers (3rd series) #9-10]
The Illuminati still met, as another Incursion occurred during Thanos' attack, and they later gathered to defend their anti-matter bombs in the Necropolis from tampering by Thanos' people. In the end, they even took prisoners. Thanos and his lieutenants Proxima Midnight and Corvus Glaive had been preserved in bio-generative amber by Thanos' lost son, and their inert forms were held in the Wakandan Necropolis. Namor and T'Challa allowed the war between Atlantis and Wakanda to go unspoken of during their meetings and Namor kept secret his efforts to send Thanos' army to attack Wakanda.
Following the war, Shuri approached T'Challa in the Necropolis and demanded to know of his absence during the fight. T'Challa's own Dora Milaje guards turned against him, warning Shuri of his meetings with Namor. Unable and unwilling to explain himself, T'Challa was severed from his kingdom and his sister. Namor, who had secretly been watching, mockingly congratulated T'Challa afterwards for becoming a king of nothing, dedicated to his people who wanted nothing more to do with him. [New Avengers (3rd series) #11-12]
Namor spent some time away from the Illuminati in the weeks that followed, soured by their association and working to rebuild Atlantis in the aftermath of Wakanda and Thanos' assaults. He was attacked by the Kree Tanalth and her Pursuer Corps, who sought a potent weapon called the God's Whisper, which Namor and several Invaders had confiscated and scattered in pieces during World War II. Namor was kidnapped to Hala to stand before the Supreme Intelligence, but his fellow Invaders Captain America, Bucky and the Human Torch came to his rescue. Namor was reminded of their brotherhood and smiled for the first time in months, although it was bittersweet considering Steve Rogers was still operating under the Illuminati's mindwipe relating to the Incursions, unaware of Namor's betrayal. [All-New Invaders #1-5]
Of course, that didn't mean things were any better when Rogers found out. After Captain America's memories were restored by exposure to the Watcher's eye, he and Namor had a tense reunion while helping the Human Torch rescue his partner Toro from Martian weapons dealers. Cap felt betrayed by his friends and was furious at Namor for allowing Strange to play around with his mind. Circumstances prevented them from having a long conversation about the situation, but their "band of brothers" was clearly fractured and Namor had lost the trust of one of his few true friends on the planet. [All-New Invaders #8-10]
The Sub-Mariner returned to Wakanda's Necropolis to find several changes. The Illuminati had built the Bridge, a device for viewing Incursions between other realities, mapping the events in an effort to find new ways of defending against the end of their universe. The Bridge's viewing flowed forward and backwards in time, allowing the Illuminati to see several events warning them that their dark ally, the Black Swan, was even more dangerous than they believed. The Swan was caged again, after an unexpectedly intense battle.
Namor found T'Challa alone at the Bridge's controls, and the two men renewed their unique association. The threat of the Incursions had turned Namor to drink in recent days, and this time he brought to share. Namor's growing pessimism about their fate clashed with T'Challa's vain attempts to maintain hope, and the two men came closer to an understanding. Although he did not specifically cite the destruction of Wakanda, Namor admitted for the first time that he regretted... many things in his life, far closer to an apology than anyone usually received from the prince of Atlantis. [New Avengers (3rd series) #15-17]
The moment would not last. A new Incursion began and the Illuminati faced their nightmare scenario -- a fully populated second Earth defended not by Mapmakers or Black Priests but by heroes like themselves. The Illuminati met the Great Society to consider the fate of two worlds. Both teams had saved their Earths in the past, but none had a method that could be reproduced this time. When the Illuminati acknowledged they had an anti-matter bomb to destroy a world if necessary, talks quickly broke down.
While Stark and Richards wished to spend more time considering other options, the Society were appalled at the very idea of the bomb, and demanded to know if the Illuminati were truly prepared to destroy a populated world to save their own. In the end, it was Namor who struck first. Seeing conflict was inevitable, he chose to initiate the horrific act on his own terms rather than wait for the choice to be forced upon him.
The Illuminati and the Great Society were almost evenly matched until Doctor Strange unleashed the power of the Blu'dakorr, the Blood Bible, and summoned an unholy creature that leeched away the life from their opponents. Strange was brought down, but the Great Society's Earth no longer had any defenders to stop the Illuminati. Unable to see another path before them, the Illuminati retreated to their Earth and prepared to activate the anti-matter bomb and destroy an inhabited world to save their own. The choice passed from one member to the next, but each found themselves unwilling to actually trigger the bomb, killing billions to save trillions. The Black Panther held his resolve the longest, reaching into the necessary amorality of the ancestral kings he was bonded to, but even he could not activate the trigger.
T'Challa appeared to believe the matter was resolved when he threw away the trigger... that the Illuminati would not destroy a world, even to save their own. But Prince Namor the First of Atlantis had yet to approach the trigger. Namor condemned his allies for their lack of conviction and for daring to place their own morality over the lives of so many at stake. He was a king and, if the fate of his people demanded the highest price from him, his morality, his conscience, his soul, then so be it, for they were his people and his responsibility.
And Namor triggered the bomb. [New Avengers (3rd series) #18-21]
The Illuminati were shellshocked that Namor actually carried through the threat they had been making ever since designing the anti-matter bombs.
T'Challa was more than shocked, he was enraged at Namor's gall in taking the choice away from him. T'Challa had sacrificed the support of the ancestral kings of Wakanda in order to maintain his honor (including the spirit of his own father), and then Namor destroyed the world anyway, making his sacrifice moot. T'Challa attacked Namor in a rage, unleashing his fury on the Atlantean and shattering whatever understanding they had reached before now. Out of spite, Namor chose this moment to reveal to T'Challa that he was responsible for Thanos' attack on Wakanda, twisting the knife that those deaths were his to claim as well.