Who is Alexander d'Arblay from Jane Austen's Letters and what is their importance?

Alexander d'Arblay was born in 1794, and he lived at Great Bookham, where he was in constant contact with the Cookes. It isn't known whether he actually met Jane Austen or not, but he is important because he is the son of Frances Burney. who was a major influence on Jane Austen as a writer. d'Arblay died in 1837.