Wild (Regency Scandal #2)
Carole Mortimer

As a result, Andrew holds himself aloof from all possibility of scandal. He does so by choosing his friends carefully and otherwise remaining aloof from Society and any romantic involvements.
He is suitably saddened when he receives a letter from a Miss Catriona McGregor, informing him that his sister and Miss McGregor's brother have both been killed in a boating accident.
It is a total shock to him when Miss McGregor then adds that the custody of the couple's four-year-old son, Malcolm, now lies with him.
Cat has no idea what to make of the aloof gentleman who arrives in Scotland claiming to be the brother of her now deceased sister-in-law, Elena. Oh, Andrew Belgrade, the Duke of Essex, is aristocratic enough to bear that title, but he is also cold and arrogant. To such a degree, Cat resists relinquishing her nephew, Malcolm, into his guardianship.
The last thing Cat expects is to feel attracted to this coldly distant gentleman.
Or for him, albeit reluctantly, to return that attraction...