Pregnant Kate, 31 on Wednesday, and entering her second trimester, is said to be keeping a low profile and spending her special day "privately," according to her office.
Having spent the recent New Year's holiday apart, Kate has since been reunited with husband William in time to spend the day with him.
Some reports suggest they are at their rented home in North Wales – a perfect secluded place for a quiet walk in the winter sunshine and fresh air with their cocker spaniel Lupo.
This time next year, she will have another family member to help her celebrate her special day.
Says royals author Judy Wade, "She has already taken the world by storm and now will cap it all by giving the Monarchy an heir, which is the culmination of their dreams."