The Alpha Fated But Rejected Mate

Fia, the only gift of her mother to her father before her death was destined to lead her pack. She was sent to the special academy where she'll receive the basic training that would define her as an Alpha heir of her Clan.
At the Academy, she got bonded to her fated-mated, a stranger whom she never knew would turn out to be the Alpha heir to the Supreme Uktena Clan, Govern by a Villain.
Meanwhile, it was taboo at the Academy as the consequence of such inter-Mating is Death. She was faced with a lot of tribulation and trials and escaped murder and allegations at the Academy.
After the death of her beloved friend at the hands of the Alpha king, Fia must travel to the underworld to meet with the keeper of souls to help revive him at a great cost.
Just when she thinks everything is fine, her life, family members and her fated mate was at stake...
But.....Why would a king order the killing of his own Son? Is he truly his son? How would she survive this whole heat and protect the lives of her loved ones?