The following entry appears in E. Cobham Brewer’s Dictionary of Phrase and Fable:
Ring. It is said that Edward the Confessor was once asked for alms by an old man, and gave him his ring. In time some English pilgrims went to the Holy Land, and happened to meet the same old man, who told them he was John the Evangelist, and gave them the identical ring to take to “Saint” Edward. This ring was preserved in Westminster Abbey.
King Edward’s ring contained a sapphire. Somehow this gem survived the interregnum of the seventeenth century, when the rest of the Crown Jewels were lost. The present day Crown Jewels date from the restoration of the monarchy in 1660. Queen Victoria had the sapphire placed at the center of the cross at the top of the Imperial State Crown. It remains there to this day.