Kate Middleton's 'smart doctor' wins hearts during latest outing with Catherine

Kate Middleton, who delighted fans with her stunning appearance at Wimbledon on Sunday, was accompanied by a person who never lets Catherine's smile fade away.

The Princess of Wales' only daughter Princess Charlotte was protecting her mom as a "smart doctor" during her royal engagement, keeping a watchful eye on the future Queen as she made her second public appearance of the year to watch the tennis tournament as patron of the All England Lawn Tennis and Croquet Club.

Princess Charlotte, 9, won hearts with her gestures during the latest outing with Kate as she was taking after her mother in being a carer as Catherine still has cancer and undergoes chemotherapy.

Ever since the Princess announced her cancer battle to the world in March, Charlotte has been going above and beyond to support her mother.

Princess Charlotte has been stepping up to help out Kate since she learned about her diagnosis.

Royal expert Jennie Bond suggested that Charlotte is particularly committed to supporting her mum, saying: "Each of the children is special in their own way: George, the adored first born, Charlotte the only girl, and Louis the baby of the family. But I think there is always a special bond between mother and daughter, and as Charlotte grows older and witnesses the shock of her mum being ill I'm sure that bond has become even closer."

Jennie told OK!: "As time goes on, I'm sure they will become more than just mum and daughter but also great companions to one another....just like Catherine and her mother Carole."

During their Trooping the Colour outing, Charlotte even had to watch over her mischievous younger brother Prince Louis to let Kate enjoy the moments.