The King has sent a warm private congratulatory 100th birthday message to former US president Jimmy Carter, expressing his admiration for his life of public service.

Mr Carter became the first former American president to become a centenarian when he reached his milestone age on Tuesday.

It is understood Charles’s message expressed warm personal greetings and great admiration for Mr Carter’s lifetime of duty and public service.

Living the last 19 months in home hospice care, the Georgia Democrat and 39th president served one presidential term from 1977 to 1981.

He worked more than four decades leading The Carter Centre, which he and his late wife Rosalynn co-founded in 1982 to “wage peace, fight disease, and build hope”.

Jason Carter, Mr Carter’s grandson and chair of The Carter Centre governing board, said: “Not everybody gets 100 years on this earth, and when somebody does, and when they use that time to do so much good for so many people, it’s worth celebrating.”

He added: “These last few months, 19 months, now that he’s been in hospice, it’s been a chance for our family to reflect.

“And then for the rest of the country and the world to really reflect on him. That’s been a really gratifying time.”

The former president was born on October 1 1924 in Plains, Georgia, where he has lived more than 80 of his 100 years.

US president Joe Biden, who was the first sitting senator to endorse Mr Carter’s 1976 campaign, praised his longtime friend for an “unwavering belief in the power of human goodness”.

In 1977, the late Queen Elizabeth II was pictured in a billowing, wide-sleeved yellow gown alongside Mr Carter, in a black tie and tuxedo, when he came to London and attended a dinner at Buckingham Palace.