Her Heartless Duke by Claire Devon

Deceiving him was wrong. Wanting him was wrong. Isaac Anderleigh was all sorts of wrong for her.

Lady Olivia harbors a fateful secret: she is dying. And in the twilight of her life, she has one lingering dream: to win the Dowager Willow’s annual dance contest. But she needs a partner. And what better match than her brother’s best friend, the irresistibly charming but tormented Duke Isaac…
Haunted by the ravages of war, Duke Isaac finds himself shunned by society and abandoned by his betrothed. His only desire is to win her back. However, his plans take an unexpected turn when Lady Olivia offers him a daring proposition…
In exchange for dancing lessons, Olivia promises to reunite Isaac with his lost love.
Except, Olivia secretly falls for Isaac herself. And is faced with a heart-wrenching choice: reveal her love or protect her heart…

*Each book in the Dukes Ever After series is a standalone story of 60,000 words that can be enjoyed out of order