Royal Dragoons Banner?

[dutto-mauri]

I bought this banner at an estate sale recently. I believe it to be a drum or bugle banner, possibly Royal Dragoons. Any info would be greatly appreciated. 

[mopata]

It is the Regimental guidon for the Royal Horse Guards from the reign of William IV.  If of the period, it would be quite a find.

[dutto-mauri]

How would I find out if it is authentic? I do appreciate your information!