The three-year-old was walking hand-in-hand with her dad, Prince William, after her younger brother's christening service when she told waiting photographers: "You're not coming", according to The Sun.
The monarch and Philip attended the christening of Louis' older siblings George at the Chapel Royal in 2013 and Charlotte in the Church of St Mary Magdalene in Sandringham, Norfolk in 2015.
Prince Harry has purchased a first edition of the famous novel, Winnie-the-Pooh, for £8,000.
The Archbishop of Canterbury, Justin Welby, tweeted Monday that he was "delighted" to be christening the third child of Prince William and Catherine.More news: Trump releases 'very nice' letter from Kim Jong Un
Kate's sister, Pippa Middleton, was also in attendance, and looked lovely in an icy pale blue. The robe is a family heirloom that dates all the way back to 1841, when Queen Victoria's oldest daughter wore it for her christening.
A close friend of the royal explained that Harry has fond memories of Diana reading him bedtime stories.
Prince Louis will wear a replica of a Victorian christening gown used in the baptisms of 62 royal babies.
Princess Charlotte sticks out her tongue while watching a Royal Air Force flypast with her brother Prince George. The Duchess of Cambridge looked feminine and romantic in a white V-neck puffed shoulder Alexander McQueen dress by creative director Sarah Burton, Jane Taylor floral-embellished woven headband hat and Jimmy Choo shoes.