The Nanny question

Anyone remember a book about a girl who lives with her two aunts, she goes to a festival in town and falls in love with a handsome young man she meets there. They are quickly married and have a son. Shortly after her son is born she wakes up and is told that that was all just a dream by her aunts. She is treated with she is crazy. After three years She accepts that what happened was nothing more than a dream. She accepts a position as a nanny to the new kings children. She becomes close to the youngest of the kings (alleged)bastards. Although there is a rumor one of the children is legitimate the child’s identity is kept secret from everyone and the children are treated equally. (As the king is expected to marry a duchess soon and her children will be expected to sit on the throne) The future wife of the king is forced to spend time with the children but the king is not present because of matters of state and wedding prep. The future wife treats the nanny and the children poorly and when the future wife hits the youngest son, the nanny smacks her. This causes a huge commotion that has the king entering the children’s wing. As she is explaining that the future wife hit the small child, both she and the king recognize one another. He was the man she married and had a son with four years ago. He embraces her and tells her they told him she died in child birth giving him a son. Then they got married