Although well-wishers only caught a glimpse of Kate, who was walking beside Prince William upon entering the church, the Duchess looked effortlessly demure as always in a recycled dark green wool coat thought to be from Sportmax, which the mother-of-two has previously wore on a visit to Edinburgh in 2016.
She accessorized the coat with a grey fur hat, leaving her trademark bouncy brunette curls down.
Meanwhile, Pippa Middleton also attended the service looked stylish in a fitted brown coat with matching heels and a hat. They were joined by their parents and brother James Middleton, who are thought to be in Norfolk to celebrate Kate's 35th birthday tomorrow.
Prince Philip and the Queen joined the family at the service in what was her Majesty's first outing in a month after suffering from a "heavy cold" over the Christmas period, causing her to miss the Christmas Day and New Year's services, and crowds of well-wishers applauded when the 90-year-old royal arrived at the church.
Kate is reportedly enjoying a quiet and private birthday to spend some quality time with her family and her two children, Prince George and Princess Charlotte. She will then go back to performing royal duties on Wednesday, where she will be visiting the Early Years Planning Unit at the Anna Freud National Centre for Children and Families. Later on the same day she will be joined by Prince William to visit a Child Bereavement UK Centre in Stratford, London.