The prince and princess lived a happy life ever after.（王子和公主从此过着幸福的生活） 这是标准的童话故事的happy ending model；套用到你的句子中：The Black Spade prince and the Red Peach princess lived a happy and carefree life ever after.
注：ever after 就是从此的意思,前面不必加 since then on!