Thor has a secret half-sister in the X-Men. Jason Aaron is renowned as one of the most important Thor writers of the modern era, so much so that Marvel Studios is now mining his Mighty Thor run for ideas; Thor: Love & Thunder will see Natalie Portman return as Jane Foster to become the Mighty Thor, just as in Aaron's stories - but now, he's shaping the comic lore in a bold new direction.
Aaron's Thor run may have come to an end, but he's now scribe of Marvel's Avengers book, and he's continuing to rewrite the Thunder God's backstory. Avengers #42 revealed Thor is actually the son of the Phoenix Force. Over 1,000,000 years ago, Odin the All-Father had an affair with an early Phoenix host, who bore his child. Odin has never exactly been presented as faithful to his wife - even in the Norse legends - so such an affair is hardly a surprise. What is rather more intriguing, though, is that Odin took the boy under his wing and brought him up as his son and heir, perhaps suggesting he really did love the Phoenix - and their relationship only ended when that particular host died.
The implications of this revelation are actually rather amusing, in that they create a strong link between Thor and the mutant race. The Phoenix is a force of death and rebirth, and it has traditionally been strongly associated with mutants. At one stage, it even took on the form of Jean Grey and joined the X-Men for a time, while the real Jean was secretly kept in a restorative cocoon. And, amusingly, as a result of various time travel shenanigans, this means Thor has a half-sister among the X-Men.
Rachel Grey originates from the alternate "Days of Future Past" timeline, and in fact, she was the daughter of Cyclops and the Phoenix Force. In that timeline, Phoenix resisted the influence of Mastermind and never became Dark Phoenix; continuing to possess the form of Jean Grey, Phoenix remained with the X-Men for years, and they even had a daughter together. Rachel inherited her mother's telepathic and telekinetic powers - and technically she was the first mutant to be described as an Omega level, although this classification is currently disputed - and upon arriving in the main timeline she claimed the Phoenix Force itself for years. Unlike most Phoenix hosts, although Rachel was tempted by the darkness, she never succumbed.
And it seems Rachel, as the daughter of the Phoenix, is essentially Thor's half-sister. No doubt this implication is probably accidental, and will be overlooked by Marvel; sadly, all signs are that Marvel has largely forgotten Rachel Grey's history and heritage, and Aaron himself has neglected to bring her into play in his current Phoenix-focused story. But X-Men fans will be more than a little amused to realize Thor Odinson and the gods of Asgard now have a direct link to the mutant race - and, in fact, to the ever-convoluted Summers family tree at that.