This was a novel I used to have quite a time ago, I never finished it but this is what I remember.
a galaxy is inhabited by alien races and one alien (who was a commanding officer and a confidant to a dignitary) is tasked with raising said dignitary's daughter after an attack by an enemy force.
Years pass and the Commander grows fond of the girl who is now clever and beautiful and wishes for his help to extract revenge on the enemies who had wronged them so long ago.
On the hard cover of the book it had a sexualized woman sitting on a throne on a desolate planet at night, a shooting star in the background along with the alien's blueish-green face subdued among the stars.
Notes of interest: late 80's/Early 90's novel, Alien commander is tasked to defend dignitary and daughter during transport, transport falls under attack, alien takes daughter and pet monkey thing into an escape pod, alien commander grows to love the girl after many years pass, basic revenge plot.
Yes it is an actual hardback storybook, no it is not an erotic novel.