haptalaon | (Reply)

From:

Aren't the likes of Rhiannon and Macha what you're looking for..? Also, Guinevere is an extension of it but in her case the connection to the myth/custom is more obscured.
You might have luck searching with horse-related search terms, the 'sacred marriage' in real life often took the form of the king copulating with an actual mare. The mythical origin of that can be traced to goddess (eg Demeter, Saranyu) transforming into a mare and then the god (eg Poseidon, Surya) getting her pregnant in that form.

(the offspring of that union, btw, are the Divine Twins, the morning and evening stars, the two horsemen who escort the Sun and the Moon. Or, in the case of Rhiannon, a son who's raised with a horse colt like they were brothers)