Queen Elizabeth once left a powerful advice for Prince William that will surely help him once he becomes king.

Prince William has always been the second in line of royal succession since his birth, and he is set to be the next king after his father Prince Charles.

With that said, there have been reports which revealed that the Duke of Cambridge has been receiving coaching on the things he should do for his next role as Prince of Wales when Prince Charles finally ascends the throne.

However, the authoritative advice he received from his great-grandmother, the Queen Mother, remains as the best guidance out of all other advices he has received so far.

In January, British magazine Tatler -- through Basia Briggs' Instagram -- shared a video of Queen Elizabeth leaving an important message to her great-grandsons, Prince William and Prince Harry, while she was inside the Clarence House.

"What single piece of advice would you give to your great-grandsons about serving as a member of the Royal Family?" the Queen Mother was asked in which she replied that she hopes that the two brothers "will put their country first, whatever happens."

Queen Elizabeth added that she was sure that the two grew and were brought up "like that." She left such inspiring words as she continued to be the backbone of the monarchy until her death in 2002.

Queen Elizabeth's Journey

Her words of advice for Prince William could have stemmed from the sudden transition she and his husband, King George VI, underwent when the tragic king Edward VIII abdicated the throne.

To recall, the former Duke of Windsor gave up his royal life and abdicated in 1936 before moving to France and spending the rest of his life with Wallis Simpson. His decision came after neither the Buckingham Palace nor the British government disapproved the twice-divorcee as his wife.

Because of this, he quit to protect the royal family from any public damages once they ignored his American wife.

After the event shook the stability of the monarchy, both King George VI and Queen Elizabeth -- as the Queen consort -- endured a lot of challenges. Fortunately, they still managed to win the trust and love of the British people once again.

During World War II, the royal family (through the words of the Queen Mother) chose to remain in the U.K. and refused to leave since the King "will never leave" the monarchy and country, as well.

She stopped her family from being relocated to Canada, which earned her great love and respect from the British public. They remained firm in protecting the monarchy even though the Buckingham Palace ended up getting bombed in 1940.

However, although they were successful in reigning the monarchy, the Queen Mother felt particularly aggrieved for all the trials they have gone through due to her husband's brother's dramatic and abrupt decision. She felt resentful to the point that she blamed the heavy responsibility of being king for King George VI's sudden death in 1952.

Despite that, Queen Elizabeth and King George's sense of duty was passed upon their daughter Queen Elizabeth II -- who continues to live her life serving the family and the whole of U.K. Like her parents, Her Majesty has chosen to dedicate her whole life serving the monarchy.

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