It might be a surprise to you, but I haven't read this book.
And I never will.
In this book, Shrek is called... Beck... and Fiona is Liona...
The synopsis:
When Liona stumbles upon Beck, the ogre's, trap and becomes his prisoner, she's determined to get away. But it doesn't take long for things to start heating up between the two. Beck is trying to protect her, and Liona can't help her body's reaction to the buff green monster. The lines between captive and captor become blurry, and the passion becomes a raging fire neither of them can put out.
and I know that one of the content warnings for that book is "incest"... (it's not Shrek and Fiona doing the incest stuff...)
Nah, I guess my Shrek fanfics are better than this.