Crowns Legacy, Book One: a sweet later in life romance

She isn't a beautiful young maiden hoping to erase the Commander's memory.
Opal Whilstead knows she has a reputation: a reputation as a bright, giving, upright woman—smiling and laughing her way through hopeless spinsterhood. It's been so long since she's had serious feelings for a man, but now she finds herself taken with the Commander Exemplar of Diachona's army.

And she regrets it.

Not only is the Exemplar a widower still longing for his wife, but he's the father of the reigning king. Even if a man of such prestige could find love again, he'd be unlikely to search for it among the kingdom's old maids. Besides, Opal dreads being found, due to a grievous secret she carries...

While this historical fantasy book does not have magical elements, the story is set in a completely fictional world.