I Married a Prince

From Fictiondb:

SECRET BABY HEIR TO A THRONE!
How could a small-town librarian with her nose in books - not the tabloids - know that the man she'd fallen for years ago was literally a prince? Or that their love child was heir to a royal throne? All Allison knew was that his seductive charm had turned her from a girl into a woman...

TEMPORARY PRINCESS
Unable to forget her, Jacob returned for one last tate of Allison's sweet lips. When he discovered his son, he proposed a temporary marriage of convenience to save his family from scandal. By law, Jacob was not allowed to marry a 'commoner.' But he was determined to bend the rules and make allison a permanent princess by Christmas...