The Duke is But a Dream by Anna Bennett

She’s a secret sensation.
Miss Lily Hartley is the anonymous mastermind behind the ton’s latest obsession: The Debutante’s Revenge, a tell-all advice column for young ladies. To keep her identity hidden, Lily delivers her columns disguised as a boy—which is well and good, until she lands in the middle of tavern brawl. As luck would have it, a devastatingly handsome duke sweeps in to rescue her.

He has no idea who she is.
Eric Nash, Duke of Stonebridge, discovers there’s a beautiful woman hiding beneath a lad’s cap, and, before long, he’s falling for the delightfully clever stranger recuperating in his house. He vows to help her find her home, even though he’s reluctant to part with her. There’s only one problem…

Neither does she.
Lily has no idea who she is. She could be a duchess or maid. Betrothed or married. There’s only one thing she does know—that her attraction to Nash is more than skin-deep, and it grows stronger every day. While Lily and Nash search to find her true identity, they just might lose their hearts to each other…