Possible Clues:

• Of late that's the sort of ring you get
• Funeral-bell
• That would sound for the little end of her in Dickens
• Ringer for dead king and girlfriend?
• Ring king's given to little girl, literally
• What no doubt sounded for the sound of Dickens' little girl
• Girl heard something indicating death
• 'The curfew tolls the . . . . . of parting day' (Gray)
• Solemn sound from king and his mistress
• By the sound of it, it might have been for little Nell in the end