Her Majesty was joined by the Duke and Duchess of Cambridge and the Duke of Sussex at Windsor Castle today - though pregnant Meghan was nowhere to be seen.
Zara and Mike Tindall, Prince Andrew, Princess Beatrice, Sophie Countess of Wessex, her son James Viscount Severn, and Peter and Autumn Phillips and were also in attendance for the seasonal service.
Kate, 37, who wore a recycled lilac Alexander McQueen coat dress, beamed as she greeted her grandmother-in-law with a curtsey outside the chapel. She previously wore the gown in 2014 on a three-week tour of Australia and New Zealand.
Earlier today the Duke and Duchess of Sussex sent birthday wishes to Her Majesty, writing on Instagram: 'Happy Birthday Your Majesty, Ma'am, Granny. Wishing you the most wonderful day! Harry & Meghan.'
Prince Harry, 34, who walked towards the chapel beside Princess Anne as opposed to his brother William, 36, managed to match his tie to his grandmother's colour scheme.
Pregnant Meghan, 37, who is expected to give birth any day now, was absent from the service. She and Harry released a statement last Thursday explaining the decision, revealing that they will also not be sharing any of the plans surrounding the birth, such as the date or the location.