A former private secretary to King Charles and Princess Diana has died aged 91.

Major General Sir Christopher Airy was hired to bring stability to the warring royal couple’s marriage in 1990, but he lasted less than a year in the role.

Sir Christopher, a former Grenadier Guards officer and distinguished soldier, was hired after a stint commanding the Army’s Household Division.

He had become a familiar face to the late Queen Elizabeth and other royals in that latter role and had, decades earlier, lined the route at Her Late Majesty’s coronation in 1953.  

But he was described as one of the then Prince Charles’ ‘worst’ appointments by royal expert Valentine Low.

Writing in his book Courtiers: The Hidden Power Behind the Crown, Low detailed how Sir Christopher was left frustrated at the increasing division between Charles and Diana’s respective staff as tensions in their marriage increased.

One contemporary described him as a ‘very bad fit’ and ‘completely on a different planet’.   

Charles and Diana announced their separation in 1992 and then divorced in 1996, a year before the late Princess of Wales was killed in a car crash in Paris. 

Major General Sir Christopher Airy, former private secretary to King Charles and Princess Diana has died aged 91

Charles and Diana announced their separation in 1992 and then divorced in 1996, a year before the late Princess of Wales was killed in a car crash in Paris. Above: The couple in Germany in 1991

Sir Christopher was born in Woolwich in 1934, the second sun of Colonel Eustace Airy.

Educated at Marlborough College, he underwent officer training at Sandhurst and was then commissioned into the Grenadier Guards.

Stationed at Windsor, he was invited to join the Queen and the Royal Family for dinner at the Castle.

Sir Christopher ended up joining the royals in a game of charades, on a team with Princess Margaret.

As his military career continued to flourish, he served as an assistant to War Secretary John Profumo, who would later resign in disgrace after a sex scandal.

Sir Christopher later commanded the Queen’s Company of the 1st Battalion in Northern Ireland in 1970 and then served as brigade major of 4th Guards Brigade in Munster, West Germany.

In 1982, he was appointed Assistant Chief of Staff of UK Land Forces.

In that role he played a key part in the decision to deploy soldiers in the Scots Guards and Welsh Guards for fighting in the Falklands War. 

Sir Christopher, a former Grenadier Guards officer and distinguished soldier, was hired after a stint commanding the Army’s Household Division. Above: Sir Christopher seen right as Prince Edward attends the Royal Tournament in Earl’s Court, 1987

After further distinguishing himself by being appointed as commander of the Household Division, Sir Christopher retired from the Army in 1989.

Sir Christopher’s appointment as private secretary to both Charles and Diana was announced in late 1989 and he started in the role in the middle of the following year.

He replaced Sir John Riddell, who had served for less than four years.

But Sir Christopher very quickly discovered that the role was not what he had expected.

One courtier, quoted in Low’s book, said the ‘fundamental’ issue was that he did not ‘fit in’.

‘He was not attuned to Charles’ growing charitable interests and struggle to understand the differences between the prince’s various organisations,’ they said.

Another contemporary said: ‘Christopher was a very bad fit. He was very charming, very posh, very Household Cavalry.

‘But he was very naive about how the world went round outside. He was completely on a different planet. 

Prince Charles and Princess Diana seen during their tour of Cameroon, March 1990

Major General Sir Christopher Airy at his desk. His departure from his role was announced in May 1991

‘He must have been miserable. We would all talk acronyms, all this charitable, voluntary sector, government stuff.

‘And Christopher was completely lost.’

Patrick Jephson, who served as Diana’s private secretary from 1988 to 1996, recounted an incident when Sir Christopher told Charles that he had to attend a particular state occasion because it was ‘his duty’.

The King was said to have ‘stiffened at the remark. He allegedly replied in sarcastic fashion: “Oh, is it?” 

Sir Christopher’s departure from his royal role was announced in May 1991.

The Queen gave him the honour of receiving him when he left. 

Sir Christopher and his wife later moved to a farmhouse in Somerset and spent the rest of their lives there.

He raised money for charity and was also chairman of the Not Forgotten Association.

He died on April 8 but his passing only emerged in recent days.