This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

Elizabeth's only sibling, Princess Margaret, was born in 1930. The two princesses were educated at home under the supervision of their mother and their governess, Marion Crawford, who was casually known as "Crawfie". Lessons concentrated on history, language, literature and music. Crawford published a biography of Elizabeth and Margaret's childhood years entitled The Little Princesses in 1950, much to the dismay of the royal family. The book describes Elizabeth's love of horses and dogs, her orderliness, and her attitude of responsibility. Others echoed such observations: Winston Churchill described Elizabeth when she was two as "a character. She has an air of authority and reflectiveness astonishing in an infant." Her cousin Margaret Rhodes described her as "a jolly little girl, but fundamentally sensible and well-behaved".
Who was Elizabeth only sibling?P