18K Yellow Gold Antique European Knot Ring with Natural Diamond Size 6-6.5

I don't know much about this ring, but it has various stamps inside the band which tell a lot about its story. All I know was that it was passed down from an aristocrat English family from approx the 1800s. 18K Yellow gold. Set with a real, natural earth diamond. Size at approx 6. Gorgeous Craftsmanship. I found it in an antique shop many years ago, but haven't reached for it in years. I'm ready to pass this treasure on!