The Rt Hon the Countess Mountbatten of Burma CBE, CD, MSC, DL or Patricia, as she is known to her friends and family, says she cannot get over how the Queen carries out such demanding duties as she reaches her 90th birthday.

Countess Mountbatten, who is the Queen’s third cousin and the Duke of Edinburgh’s first cousin, said: “Despite her advancing years, the Queen still does her very best to fulfil her pledge to serve her country.

“I am two years older and I can’t imagine how she can go on doing so much. She has cut down a little bit but there are many times when she attends state functions - all that standing and meeting everyone must be exhausting.

“She considers it is a job for life and she has always has done her best - she always will do.

“We’ve had an incredible 63 years of her service and I believe the Queen is somebody who everybody can look up to, admire and love.

“Her 90th birthday is an opportunity to show her our affection, admiration and gratitude for what she has done for everyone. She has been remarkable.”

Countess Mountbatten, 92, has lived in Mersham, near Ashford, for 70 years. The Queen and the countess spent ‘many happy times together’ when their children were growing up.

They also supported each other through some of the most extraordinary events of the late 20th century including the assassination of the Countess’s father, Lord Louis Mountbatten, when a bomb blew up his boat near Sligo, in the north west of Ireland.

The countess was on the boat and escaped with injuries but lost one her twin sons, Nicholas, and her mother-in-law to the blast. The death of Diana, Princess of Wales and the three failed marriages of the Queen’s children were also times of ‘immense sadness’.

Countess Mountbatten said: “The Queen coped well with family difficulties, we must remember the Royal Family goes through problems like most other families.

“She has overcome all of this and it is now lovely to see her smiling all the time. She does have a most marvellous sense of humour. I believe it keeps her going.”

Countess Mountbatten is also godmother to Prince Charles and has enjoyed seeing his sons grow up.

She said: “Kate Middleton was a happy choice for Prince William. He knew she was the person for him and the feeling was mutual. They make a lovely family and their children are enchanting.

“I also think Prince Harry is doing well after the high jinx of youth and he is showing a very good side to his nature.”