The Decadent Duke

Description for THE DECADENT DUKE by Virginia Henley:

Lady Georgina's four sisters have all married prominent dukes or earls, and much to her dismay and frustration, she is expected to make an even better match. Georgina's mother has no doubt who her daughter should marry: Francis Russell, Duke of Bedford. The dull duke does absolutely nothing for Georgina, but despite her best efforts, she finds herself engaged to marry him.

But Georgina cannot deny the passionate sparks between herself and a different man - John Russell, the duke's younger brother....

This is #1 in Peers Of The Realm Series.