BIOGRAPHY - page 14
Matters came to a head after their Western adventure. "Looney Tunes" Panther collapsed, and Nightshade was unable to do anything to stabilize his condition. The dying future Black Panther had to be placed back in stasis to preserve his life. The present day T'Challa had begun experiencing tremors and hallucinations as well, traced back to the beating he received at the hands of Iron Fist. The degenerative brain aneurysm which was killing his future self had already 
been contracted by the present king. His hallucinations often took the form of Magneto, for T'Challa was still haunted by Ororo's words that he would end up like the Master of Magnetism. In his anxiety over the situation, T'Challa finally came clean with Monica over why he called off their engagement. He explained that meeting a future version of himself dying of a terminal illness meant he could not offer Monica a full life. Monica left Wakanda, understanding T'Challa's decision and fully expecting to see him again soon, regardless of their relationship status. That was not to be.
Meanwhile, Queen Divine Justice learned that M'Baku and the Jabari were being held without trial after the conflict in the Crystal Forest. Vibraxas informed her it was only by the king's mercy they still lived and had not been executed. Queen felt responsible for the Jabari people, however, and in her viewpoint imprisonment without trial for worshipping the wrong god meant the Jabari were political prisoners being denied their fundamental rights. Queen and Vibraxas decided to free 
M'Baku and his men, with a promise extracted from them that they would return to the Crystal Forest and do nothing to seek vengeance on Black Panther. Man-Ape pledged to honor his cousin's wishes, but he still made contact with T'Challa before departing. He did not try to assault the Black Panther directly, but instead shattered the future Black Panther's stasis cell. The second T'Challa died on the operating table hours later, seemingly sealing the fate of the present king.
Murder of the king was an act of war in any culture, especially when the king was still alive to seek vengeance. The Black Panther assembled all the tribes of Wakanda, Okoye, Zuri, Venomm, 
W'Kabi, the Prowlers, the N'Yami cruisers and every single force under his command to march on the Crystal Forest. Queen Divine Justice and Vibraxas stood between the armies of Wakanda and Jabari and tried to negotiate a peaceful solution, but neither T'Challa nor M'Baku were interested. T'Challa addressed Queen purely as a rogue Dora Milaje and denounced her for her treason against the throne. Hot-headed Vibraxas lashed out at the king, whose Magneto hallucination returned and provoked him into fighting as well. Queen still hoped for peace, and tried to help Black Panther up when he fell. It was then, in a moment of hallucination, that T'Challa lost control completely and struck Queen while believing her to be Magneto.
T'Challa immediately regretted his actions and fell to a seizure as his aneurysm progressed. The Jabari and Wakandans fell upon each other in a massive bloodbath that only ended when the 
terminally injured Chante broadcast a plea using her Kimoyo card. Stabilized from his dementia by a field medic and more ashamed than he had ever been in his life, T'Challa accepted the petition from Queen to free her people, ceding the lands of the Crystal Forest to the Jabari. Queen Divine Justice was saved, but she would never again be Dora Milaje. After these errors and losses, T'Challa abandoned his throne and left the Wakandan Parliament in charge of his country. [Black Panther (3rd series) #48-49]
T'Challa was missing for months and presumed dead by the world at large. He began living a destitute life in the Leslie N. Hill Housing Project in Brooklyn, attended to only by Okoye. Meanwhile, a police officer named Kevin "Kasper" Cole began impersonating T'Challa. A friend of T'Challa's old ally Sgt. Tork, Kasper lifted a damaged Panther costume from Tork's place, which the sergeant had picked up after Black Panther discarded it fighting Nightshade years ago. 
Kasper was on suspension after being caught between the 66 Bridges gang and corrupt officers on the force, and he needed a disguise to track down who was responsible for his squad getting shot up. T'Challa and Hunter both took an interest in Kasper's actions, though their true intentions were largely inscrutable. Still, interacting with Kasper provoked T'Challa out of his brooding, leading him to return to the throne. [Black Panther (3rd series) #50-56]
Scorpio of the Zodiac opened up a series of dimensional warps which swallowed up most of Earth's capitols, throwing the world into chaos. Black Panther and Gyrich returned to the Avengers as what remained of the United Nations passed a measure ceding authority of the planet to the Avengers in this time of crisis. With Captain America at the head of the table and other monarchs like Namor and Thor lending support, the Avengers weathered the crisis admirably and managed to reclaim Earth's capitols and leadership from the Dimension of the Ankh. In the aftermath, 
Avengers Mansion was recognized as Avengers Embassy, given the same recognition as a sovereign nation among the United Nations. T'Challa chose to remain on the Avengers' roster after that, although he still wasn't trusted by some of the membership, especially Iron Man and Warbird. Stark accused T'Challa of remaining with them solely to gain access to the United Nations security codes and files, and Black Panther merely told him to believe what he wanted. [Avengers (3rd series) #57-61]
Although Black Panther had more-or-less acknowledged him and given his blessing, Kasper Cole needed more than a second-hand costume to continue operating as a junior Black Panther. He was working an angle trying to rescue the kidnapped son of his corrupt lieutenant in order to get the man's help bringing down the 66 Bridges responsible, but needed more of an edge. Kasper petitioned T'Challa for the tribal challenge and the right to eat from the heart-shaped herb. T'Challa tried to dissuade Kasper from this path, but relented and constructed a series of trials in New York to test Kevin's mind, body, and soul akin to the Rites of Ascension used in Wakanda.
A complication arose when Erik Killmonger finally awakened from his coma, and reassumed the role of tribal chieftain. Whereas T'Challa was willing to waive certain standards for Kasper's challenge and the Rite of Ascension in his role as chieftain by default, as actual chieftain it was within Killmonger's rights to kill Kasper in ritual combat in response to the challenge. Short of killing Kasper, Killmonger also offered to make a side deal with the officer. He had synthesized his own non-toxic version of the herb, which was less likely to kill Kasper when he took it, and offered to find the missing kid for him. Kasper ultimately chose to avoid being in Killmonger's debt and found the kid himself, but discovered in the process that T'Challa had already done so. Finding the child and refusing to be corrupted were the final stages of his Rite of Ascension, and so T'Challa gave the full blessing of the Panther God upon Kasper. He was deemed an acolyte in the Cult of the Black Panther, and given the new costume and identity of the White Tiger. [Black Panther (3rd series) #59-62]
[Note: This was the last mention of Killmonger as tribal chieftain of Wakanda. All subsequent stories once again treated T'Challa as both king and chieftain, leaving Killmonger's position an unresolved plot thread. Similarly, no further reference was made to T'Challa's terminal brain aneurysm. Presumably, it was treated successfully.]