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LONDON (Reuters) - Britain’s Prince George, the great-grandson of Queen Elizabeth and third-in-line to the throne, started school on Thursday but without his pregnant mother Kate to support him because she is suffering from severe morning sickness.

George, 4, was taken by his father, Prince William, from their Kensington Palace home to Thomas’s Battersea school in southwest London, which says its most important rule is to “Be Kind” and charges almost 18,000 pounds ($23,490) per pupil per year.

“We expect our pupils to make impressive progress as a result of their own hard work, the best efforts of their teachers, the judicious support of their parents and the encouragement of their peers,” the school says on its website.

A nervous-looking George, wearing a school uniform of dark shorts and a navy jumper with red trim, held his father’s hand as the Head of Lower School, Helen Haslem, escorted the royal duo to his classroom.

His mother Kate missed the occasion due to acute morning sickness and has canceled other engagements this week after the palace announced on Monday that she was expecting her third child.

Like his parents, George and his younger sister Charlotte have already appeared on the front covers of magazines around the world and this summer they traveled on official royal tours of Poland and Germany where crowds cheered them.