Sarcoids/warts?

[Switcheroo]

Just discovered what looks like a wart on my youngster. Just under his tail, on his backend. It's perfectly circular, dark, and about the size of the tip of your thumb. Wasn't sure if this was just a blemish because in four months of having him I've never noticed it before! I'll get a picture but does anyone have any experiences with this sort of thing or know what it might be?

Thanks in advance to anyone who can help x

 

[AmyMay]

What colour is the horse and how old?

 

[Switcheroo]

he's quite unusually coloured... a dark bay with lots of grey hairs and some white spotting here and there. A 3yr old.

 

[AmyMay]

I'd want the vet to look at it.