Prince William attends star-studded Earthshot Prize ceremony without Princess Kate

Kate stayed home in the U.K. while William traveled to Singapore.

Prince William walked the green carpet Tuesday alongside stars including Cate Blanchett, Sterling K. Brown and Hannah Waddingham at the awards ceremony for his annual Earthshot Prize.

William attended the ceremony in Singapore without his wife Kate, the Princess of Wales, who did not attend the event for a very personal family reason.

According to the Prince of Wales, Kate, who shares three children with William, stayed home in the United Kingdom to help their eldest child Prince George prepare for his school exams.

"Catherine is very sorry she can't be here," William said in a speech Monday at the United for Wildlife Global Summit, which was organized by The Royal Foundation, the organization that supports the Waleses' charitable endeavors. "She is helping George through his first set of major exams."

George, 10, second in line to the throne behind his dad, is currently a student at the Lambrook School in Berkshire, a preparatory school for children ages 3-13 in South East England.

Once George turns 13, he could then potentially follow in William's footsteps by attending Eton College, which he toured earlier this year with William and Kate, according to ABC News royal contributor Victoria Murphy. The all-boys boarding school, which also educated George's uncle, Prince Harry, is located near the Waleses' home in Windsor.

Kate is typically by William's side at the annual Earthshot Prize awards ceremony, which was held last year in Boston.

William launched the Earthshot Prize in 2020 as a way to honor the most innovative and impactful climate solutions.

In Singapore Tuesday, winners were announced in each of the Earthshot Prize's five categories, with the winners earning grants of over $1 million.

William's father King Charles III was also back home in London this week marking an important milestone.

Charles and his wife Queen Camilla on Tuesday attended the State Opening of Parliament for the first time since Charles became king.

Charles wore the Imperial State Crown, which the public saw at his coronation in May, and read the King's Speech, a first after more than 70 years following the reign of Charles' mother, the late Queen Elizabeth II.