Dombey and Son was begun at Lausanne in the summer of 1846, and finished in Paris early in 1848. When Dickens had sent off the copy for the last monthly part, he remembered that when he was tying up the loose ends he had forgotten to say anything about Florence's dog Diogenes. On 25 March 1848, he wrote to the faithful Forster, who was attending to the press in London.
Note from Charles Dickens, from Literary Anecdotes