A Royal Affair, by Stella Tillyard

By 1775, five of George III's eight siblings were dead. The 34-year-old king was estranged from two more: his brothers, princes William and Henry, whom he neither spoke to nor saw, as they had made secret marriages to commoners without his consent. Yet from the newspapers, Stella Tillyard points out, one would have formed an idyllic picture of the royal family's private life.

The one sibling with whom he remained on good terms was his sister Augusta. The widely reported domestic drama surrounding her birth in 1737 introduces one of Tillyard's recurring themes - proletarian appetite for royal stories. "Private life had become a tradeable public commodity and a culture of celebrity was being born." As Augusta's siblings became more numerous - the first royal family brought up in England for over a century - they represented both opportunities to make dynastic links through marriage, consolidating Britain's position in the world, and the potential to strengthen the bond between throne and people. However, as Tillyard demonstrates, this position also rendered them liabilities. The headaches his family were to cause George III put Elizabeth II's annus horribilis in the shade.

The expectation that George and his siblings would marry on the basis of political expediency at once legitimised the public's interest in their private lives, and resulted in marriages which were often doomed. Hence a highly combustible situation: here was a living soap opera where not only were duty and desire frequently at odds, butdomestic disharmony could have far-reaching political consequences.

Nowhere is this more evident than in Tillyard's account, which dominates the book, of the unhappy contract between George III's youngest sister, Princess Caroline Matilda (later Mathilde), and King Christian VII of Denmark. Aged 15, she married the 17-year-old king, but the breakdown of their union almost led to war between the two countries.

A stranger in a strange land, Caroline Matilda arrived in Denmark to find her new husband was not only indifferent to her, but insane. Christian's position as absolute monarch inhibited any of his friends from attempting to restrain his frightening excesses. His young queen, having dutifully produced an heir, at the age of 18 sought solace in the arms of her husband's favourite - Johann Struensee, physician and philosopher. As Christian's mental illness progressed, Caroline Mathilde and Struensee began effectively to rule in his stead.

Retribution was swift. Struensee had his hand chopped off, then his head and genitals. His body was quartered and his various parts stuck on spikes for crowds to marvel and gulls to peck at.

Caroline Mathilde was imprisoned in Elsinor; a location sufficiently endowed with meaning for a British public which had recently adopted the Bard of Avon as a national treasure to ensure her case would be followed. Concern became pressure on George III to relieve his sister's sufferings, if not restore her crown. News of an agreement that Caroline Mathilde would be allowed to live in exile reached Plymouth just in time to prevent a fleet of warships setting sail for Copenhagen.

Tillyard's assured narrative vividly reconstructs the intellectual as well as the political context, and the critical role played by the growing interest in the private lives of public figures. She does not dwell on George III's mental illness, nor particularly on his life. What she does especially well is to enable the reader to identify with his worldview.

His guiding aim was simply to serve his country as he had promised in his Coronation Oath. The still centre of this engaging account is his highly developed and unswerving sense of duty to his people.

Sarah Burton's 'A Double Life: a biography of Charles and Mary Lamb' is published by Penguin