The Fake Heiress Is the True Princess, and the Ruthless General Has Her Wrapped Around His Finger

[One-on-one romance, sweet and doting, everyday life, equally strong leads, high combat ability, marriage before love, a sweet little romance] What a joke. I lived for seventeen years before learning I wasn't the biological daughter of the Yan family. Who would have guessed my real parents would be the Grand Princess and a Duke? The younger sister who traded lives with me says outright that she likes my fiancé. Fine, you can have my parents too. Take my fiancé as well. It's all yours, yours, yours. As for me, I marry the jade-faced demon general whom all the noble young ladies in the capital fear. Who knew he wouldn't be as cold and heartless as the rumors claimed? Instead, he's considerate and gentle with me in every way. So why has my dear little sister suddenly started regretting it?