If the woman he married was an Other
This is best explained knowing the bigger picture
The wife wasn't an Other - she was a CotF - their offspring were the unnatural Others -as there was some really evil-intended magic going on -- a result of the pact - The Night's King could have been Aegon the Conquerer who later became LC most likely (a leader is his character reincarnation pathway), then all the other Others (+/-13 or so of them) are the successive Targaryen Kings (to include Tywin, as he really was King in Robert's drunken stupor), this is why tywin went through the Gate of the Gods as his funeral procession left King's Landing to Casterly Rock - Tywin ascended after death to become a God - an Other
The truths of those old stories aren't true - lost in time and purposely twisted - timelines aren't true - what really happened was more sinister - child blood sacrifice to create a super being - the Others - who are really just dead King Targaryens - everything is spelled out in the original book A Game of Thrones -if you go back and re-read AGOT with an alt interpretation of every sentence that contains the word Other .,. or other you will see the truth of the story revealed
The war had raged for close to a year. Lords great and small had flocked to Robert's banners; others had remained loyal to Targaryen. The mighty Lannisters of Casterly Rock, the Wardens of the West, had remained aloof from the struggle, ignoring calls to arms from both rebels and royalists. Aerys Targaryen must have thought that his gods had answered his prayers when Lord Tywin Lannister appeared before the gates of King's Landing with an army twelve thousand strong, professing loyalty. So the mad king had ordered his last mad act. He had opened his city to the lions at the gate. -A Game of Thrones - Eddard II
The Mad King Aery's unknowingly allowed another ancient Valyrian family bloodline, the Lannisters, to take control of the crown
"The Others take your honor!" Robert swore. "What did any Targaryen ever know of honor? Go down into your crypt and ask Lyanna about the dragon's honor!"
"You avenged Lyanna at the Trident," Ned said, halting beside the king. Promise me, Ned, she had whispered.
-Lyanna was used by the Targaryens to birth a dragonGodhuman - the Prince that was Promised (in the viewpoint of Rhaegar - but this PtwP has several meanings depending on who is referring to it) - which is what Targaryens do - remember Dany's child Rhaego was stillborn born with wings and a tail - I suspect she had to have a cessarian section because the dragon would have killed her at birth - she was not "naturally biologically hipped" to birth a dragon - thus frequent deaths at child birth from Targaryen male parentage - this is why Dorne is so pissed - Elie was ruined when she birthed a dragonSpawnAttempt
"Every case is different, and every case is alike. Lord Jon's death was no stranger than any other." -Pycelle
Davos would have given much to know what he was thinking, but one such as Velaryon would never confide in him. The Lord of the Tides was of the blood of ancient Valyria, and his House had thrice provided brides for Targaryen princes; Davos Seaworth stank of fish and onions. It was the same with the other lordlings. He could trust none of them, nor would they ever include him in their private councils. They scorned his sons as well. My grandsons will joust with theirs, though, and one day their blood may wed with mine. In time my little black ship will fly as high as Velaryon's seahorse or Celtigar's red crabs.
Davos' doesn't realize that the nature of Valyrian blood is that it tries to remain true through inbreeding - to elicit dragonGodMan
Or had Stannis found one egg on Dragonstone? Even if he has an egg, how can he hope to quicken it? Baelor the Blessed had prayed over his eggs, and other Targaryens had sought to hatch theirs with sorcery. All they got for it was farce and tragedy.
Samwell is getting closer to answers
Margaery was dancing with her cousin Alla, Megga with Ser Tallad the Tall. The other cousin, Elinor, was sharing a cup of wine with the handsome young Bastard of Driftmark, Aurane Waters. It was not the first time the queen had made note of Waters, a lean young man with grey-green eyes and long silver-gold hair. The first time she had seen him, for half a heartbeat she had almost thought Rhaegar Targaryen had returned from the ashes. It is his hair, she told herself. He is not half as comely as Rhaegar was. His face is too narrow, and he has that cleft in his chin. The Velaryons came from old Valyrian stock, however, and some had the same silvery hair as the dragonkings of old.
Maergery identifies another bastard child (hint: they are everywhere)
The sight had filled him with disquiet, reminding him of Aerys Targaryen and the way a burning would arouse him. A king has no secrets from his Kingsguard. Relations between Aerys and his queen had been strained during the last years of his reign. They slept apart and did their best to avoid each other during the waking hours. But whenever Aerys gave a man to the flames, Queen Rhaella would have a visitor in the night. The day he burned his mace-and-dagger Hand, Jaime and Jon Darry had stood at guard outside her bedchamber whilst the king took his pleasure. "You're hurting me," they had heard Rhaella cry through the oaken door. "You're hurting me." In some queer way, that had been worse than Lord Chelsted's screaming. "We are sworn to protect her as well," Jaime had finally been driven to say. "We are," Darry allowed, "but not from him." Jaime had only seen Rhaella once after that, the morning of the day she left for Dragonstone. The queen had been cloaked and hooded as she climbed inside the royal wheelhouse that would take her down Aegon's High Hill to the waiting ship, but he heard her maids whispering after she was gone. They said the queen looked as if some beast had savaged her, clawing at her thighs and chewing on her breasts. A crowned beast, Jaime knew.
This is where Rhaella gives birth to a dragonGodMan - possibly a magic shadowbaby-like Melisandra for super sinister purposes - once a woman gives birth to such a beast, their own magic dissipates - and they are sent to Braavos (brothel) I suspect - to become a Targaryen version similar to what the Khals do with their Queens -- the Dosh khaleen
Read this - the whole story is laid out - mostly -- https://asearchoficeandfire.com/?q=Other+Targaryen&scope[]=agot&scope[]=adwd&scope[]=tmk&scope[]=acok&scope[]=twow&scope[]=twoiaf&scope[]=asos&scope[]=thk&scope[]=trp&scope[]=affc&scope[]=tss&scope[]=tpatq
At some point you realize that Ned understood all this and he knew he had to die to become a stronger agent against the true evils of the Others and the Targaryens -- through his sword ICE (now Oathkeeper and Widow's Wail) - -Widow's Wail has been a neglected story