What's the relationship here(horse family tree)

[HorseMaid]

Randomly discovered that a horse that lives near mine and looks identical is very closely related, but I can't put my finger on the technical term for the relationship because it hurts my brain.

So if my horse's Sire is the other horse's grandsire, and the other horse's dam is my horses grand-dam, what does it make them?

 

[Cortez]

Your horse is his uncle?

 

[HorseMaid]

I suppose that could be it although it seems too obvious!

 

[Cherryblossom]

And his nephew!

 

[Dave's Mam]

They're uncle AND nephew to each other.

 

[HorseMaid]

That would be auntie and niece as both mares bit sort of makes sense!

 

[poiuytrewq]

What’s your horses name op!

 

[Roasted Chestnuts]

Sounds like it’s a Welsh ??