The Alpha Prince by Victoria Sue

The Askaran desert can no longer sustain the secret hybrid population of wolves bred from those sent there to die for their crimes. Justice knows the time has come to lead his wolves to a new life, but soon realizes his pack could never be governed by nor swear fealty to the cruel and despotic Alpha of Solonara—Darius—so he hatches a plan to fight and ultimately kill the Alpha, his heir, and take over the territory.
Cashel should not exist. It was unheard of for an Alpha-heir to be born an omega, and Darius has made every day a torment for his son. After spending years failing to breed another heir, and desperate not to have to give his territory away to another pack, he finally turns his attention back to Cashel and a whole new nightmare begins.
Justice’s whole life has been about righting a wrong and delivering the very thing he was named for. Meeting Cashel, and finding out he is his true mate, sends his carefully constructed plans and promises up in flames. When he discovers Darius’s cruelty runs deeper than any of them imagined, he is faced with a last desperate choice between his love for Cashel or his loyalty to his people.