Metamorphoses Book 2: Callisto
Jove went through the heavens and earth repairing the damage that the great fire had done. While he was on Earth, he saw a nymph, one of Diana's chaste followers, and fell in love. Disguising himself as Diana, he approached Callisto. She greeted him warmly believing him to be her favored goddess, but when he kissed her savagely, she knew that he was someone else in disguise. She fought against Jove, but he overpowered her and had his way with her before disappearing.
Soon after, Diana and her followers passed by and Callisto tried to hide the shame of her violation. For nine months she kept her secret hidden until one day when Diana and her nymphs were going swimming in a stream. Callisto was reluctant to undress, and so the other nymphs ripped her clothes off. When they saw her pregnant body, Diana banished her from their cult. Callisto bore a son, Arcas, and Juno was furious. She'd been waiting to exact her revenge, and so when the nymph gave birth to a boy, jealous Juno transformed Callisto into a bear.
The changed woman roamed the woods and countryside with the body of a bear and the mind of a woman until her son was 16 years old. They encountered each other in the woods, and Callisto recognized her son. She stared at him intensely, and this frightened the boy because he had no idea that the bear staring him down was his mother. Arcas raised his javelin to kill the animal, but Jove stopped his hand. To prevent this crime from occurring, the greatest of gods swept both Callisto the bear and her son, Arcas, into the sky and made them neighboring constellations, the Great Bear and the Little Bear.
Juno saw this and was furious because Jove had made one of his paramours immortal in the stars, but there was nothing she could do about it.