The Royal Court of Sweden released new official portraits of Prince Oscar to celebrate his fourth birthday.

Prince Oscar, the only son and youngest child of Crown Princess Victoria and Prince Daniel, turned four on Monday. In honour of the occasion, two new black-and-white photographs of the young royal were shared by the Swedish royal court on its official Instagram account.

In his monochrome portrait, the four-year-old was seen smiling gazing out of the window, dressed in a collared T-shirt and grey knitwear. In another picture, he was seen posing with older sister Princess Estelle, eight. The royal siblings were flashing adorable grins while resting their chins on their hands.

"Today, Prince Oscar turns 4!" the post was captioned on the Kungahuset Instagram account.

In the photographs, the brother-sister duo was seen wearing the same clothes that they wore in the portraits released on Princess Estelle's eighth birthday on Sunday, February 23. While Oscar was sporting a grey jumper over a white shirt and cream chinos, Estelle was wearing a stunning off-white high-necked dress with a blue floral pattern. The pictures were taken in mid-February at Haga Castle outside Stockholm, where Estelle and Oscar live with their parents, reports People.

Oscar, the Duke of Skåne, is third in the line of succession to the Swedish throne, after his mother Victoria and his sister Estelle. A grandson of King Carl XVI Gustaf and Queen Silvia and younger child of future Queen Victoria, he was born on March 2, 2016, at Karolinska University Hospital in Solna, Stockholm.

Before Estelle, another child from the Swedish royal family celebrated a birthday last month. Princess Leonore, the oldest child of Princess Madeleine and Christopher O'Neill, celebrated her 6th birthday in Miami on February 20. Holding the title of the Duchess of Gotland, Leonore is eighth in the line of succession to the Swedish throne. At the time of her birth, she was fifth in line.

Sweden Prince Oscar christening
Prince Oscar, Duke of Skane, is seen after the christening ceremony Andreas Rentz/Getty Images

While Estelle and Oscar retain their titles of Royal Highnesses, as the children of the future queen, but Princess Leonore along with the rest of the grandchildren of King Carl will no longer be styled with the title. The decision was taken in October last year.