Question: Lady Margarita Elizabeth Rose Alleyne Armstrong-Jones is the only daughter of an English furniture maker who is 18th in line of succession to what?  
Sentence (from "David Armstrong-Jones, 2nd Earl of Snowdon"): The son of Princess Margaret, Countess of Snowdon, and of Antony Armstrong-Jones, 1st Earl of Snowdon, he is a grandson of King George VI and is 18th in line of succession to the British throne, the first in line who is not a descendant of Queen Elizabeth II.
Relevant evidence: Yes