Somehow... I have a feeling that the previous third princess had promised that white haired man he will became her second consort when he comes back to the capital when she was little... He just appeared, and I already kinda feel guilty on behalf of the princess lol
(I'm pretty sure I had read somewhere that chinese prince of that time can have several second consorts, if my theory is true, I sure hope she can make that guy her second consort too...)