Could it be that he himself was in love with Lady Ethelrida?
She had been too preoccupied with her own affairs to be struck with those of others, but now as she looked back, he had shown an interest which was not in his general attitude towards women.
How her mother had loved him, this wonderful brother! It was her abiding grief always, his unforgiveness,--and perhaps, although it seemed impossible to her, Lady Ethelrida was attracted by him, too.

Yes, that must be it.

It was to be connected with the family, to make his position stronger in the Duke's eyes, that he had done this cruel thing.

But, would it have been cruel if she herself had been human and different?
He had called her from struggling and poverty, had given her this splendid young husband, and riches and place,--no, there was nothing cruel in it, as a calculated action.

It should have given her her heart's desire.