Stretton by Henry Kingsley

I think that Roland was secretly angry with the elder Mordaunt as to his good-humouredly bringing him to beck about Mary Maynard. Miss Mordaunt was much too fine a young lady to have any mistakes made about her of any sort or kind. He would have been profoundly delighted that Roland should marry his sister, and would be very glad to see his friend happy with Mary Maynard. Only John Mordaunt, by far the shrewdest of the five boys, was determined that he should make up his mind.

Roland and Ethel had been brought up together, and had always called one another by their Christian names, and as Roland would have said, were as brother and sister. So would not Ethel have said. Ethel's secret was known to two people, and guessed by a third.