March 14 is Mother's Day in the United Kingdom, and the royal family has been marking the occasion with social media posts. Mothering Sunday, known as Mother's Day, is celebrated on the fourth Sunday of Lent. On her first Mother's Day, Princess Eugenie shared a new photo of her baby son August on Instagram. The photo shows August lying on a blanket in a field of daffodils and in her caption, Princess Eugenie wrote "I'm so excited to be August's mum and as you can see I'm enjoying my first Mother’s Day."