Fire From Heaven by Mary Renault

At twenty, when his reign began, Alexander the Great was already a seasoned soldier and a complex, passionate man. Fire From Heaven tells the story of the boy Alexander, and the years that shaped him. Resolute, fearless, and inheriting a striking beauty, Alexander still needed much to make him The Great. He must survive – though with lifelong scars – the dark furies of his Dionysiac mother, who kept him uncertain even of his own paternity; respect his father’s talent for war and kingcraft, though sickened by his sexual grossness; and come to terms with his heritage from both.