A Promise to Repay(2006)

Fukushuu no Daishou

Four years ago, Kate lost her beloved brother, her only remaining family. To exacts her revenge on Aidan, the man who drove her brother to his death, she attends his wedding and messes up the ceremony by claiming to be his wife. But Kate was mistaken-the man she truly wanted revenge upon was Aidan's twin brother!

(Source: Harlequin)