The seven-year-old enjoyed a school summer holiday break to the Midlands to join spectators at the Sandwell Aquatics Centre.
William and Kate, the Duke and Duchess of Cambridge, arrived with their daughter who enjoyed a morning of sport.
The royals were cheering and applauding alongside the crowd for England 1,500m freestyle hopeful Luke Turley.
Princess Charlotte looked as though she had enough of the swimming at one point when she rested her head in her hand.
After rolling her eyes following a comment from her father, Charlotte then cracked a smile as Turley’s heat came to a close.
The trio arrived shortly after the Earl and Countess of Wessex and their children, Lady Louise and James.
Kate, dressed in a white blazer and trousers, embraced Edward, Sophie and their children before taking her seat next to Charlotte.
The Duchess was pointing and explaining things to her daughter, while William held one of the official programmes.
Princess Charlotte, who appears to be following in her mother's footsteps as a sports fan, has already had quite the week, sending a good luck video message to the Lionesses ahead of their Euros win on Sunday.
Today, she is wearing a casual navy and white striped dress with a white collar, with neat pigtails plaits.
They were greeted by the Commonwealth Games' mascot, Perry the Bull, when they arrived.
Charlotte appeared curious about her surroundings and the people around her at Birmingham University, and a little apprehensive at times, but received a reassuring arm around her shoulder or word in her ear from William, and held Kate’s hand at other moments.
The young princess revealed gymnastics was the sport she liked most and joined a nutritional workshop helping her parents place pictures of foods like nuts, bread and grapes into the right groups, whether protein, carbohydrates, antioxidants or healthy fats.
At one point Charlotte was asked to update a Team England medal board and added a bronze, won in the men’s team table tennis event, and a silver from the lawn bowls men’s pairs.
She was also taken by William and Kate to events at the Commonwealth Games and was photographed grinning during swimming heats and later joined her parents to watch a hockey match.
The Royal Family have been supporting the Commonwealth Games this year, with the Wessexes set to attend most days.
The Prince of Wales and Duchess of Cornwall attended the opening ceremony, arriving in Charles' cheese and wine-fuelled Aston Martin.
As Head of the Commonwealth, she is invested in the ongoing success of the tournament and will pay close attention to the stories and successes of its members.
The Cambridges are set to spend the day in Birmingham, and will join a session of young sportsmen and women to hear about their training.