Kathleen Kennedy and her elder brother JFK were the grandchildren of upwardly mobile Irish Catholic immigrants. John F. Fitzgerald, ‘Honey Fitz’, became mayor of Boston, and Patrick J. Kennedy was a saloon-keeper and failed senatorial candidate who sent his sons to Harvard. ‘Kick’ was the fourth child, nicknamed for her ebullient personality, but born just as her mother, Rose, was thinking of leaving her serially unfaithful husband, Joe Kennedy Snr, who made his huge fortune from Hollywood studios and booze. Kick spent her early years schooled at, and confined to, convents, except when the whole family escaped to Hyannis Port or Palm Beach.

So when her father managed to wangle the post of Ambassador to the Court of St James from President Roosevelt in 1938, moving his nine children to London, Kick felt liberated. Thanks to her social-climbing parents and her own charm, she was taken into the bosom of the British aristocracy. This gum-chewing, plain-looking all-American girl, and her older sister Rosemary, came out in the London season of 1938, when Kick was hailed as debutante of the year. Three years later, fearing that the cerebrally challenged Rosemary would be subject to sexual predators, Joe and Rose arranged for her to have a frontal lobotomy, which left her in a vegetative state until her death in 2005. The curse of the Kennedys had struck; and Kick’s own story was almost equally sad.

Paula Byrne’s Kick details the life of one of the few members of this family who has not yet been subjected to the biographer’s beady eye. It is bad luck that her enjoyable, relatively sober book was pipped at the post in America a month earlier by Barbara Leaming’s tawdry Kick Kennedy.

Kick fell utterly in love with ‘Billy’, the Marquess of Hartington, heir to the dukedom of Devonshire, and a Cecil on his mother’s side. The devout Catholic Kick was to marry into the Cavendishes, historically ‘perhaps the most anti-Catholic family in England’, says Byrne. They were together only five weeks between their wedding on 6 May 1944 and Billy returning to the Coldstream Guards in time for the Second Front, to be killed in Belgium by a sniper’s bullet on 9 September. Four years later, Kick, Marchioness of Hartington, fell for a married roué, the 8th Earl Fitzwilliam, Peter Wentworth-Fitzwilliam. On 13 May 1948, having tried to negotiate a marriage arrangement with Joe Snr in Paris, the reckless earl insisted, against the advice of his pilot, on flying the private plane to Cannes. He, Kick and the reluctant pilot perished in a storm in the Cévennes. The Kennedys’ favourite daughter was 28 when she died.

Rose, whose voice was ‘like a duck with laryngitis’, was poisonously pious, her doctrinaire Catholicism outweighing even her social ambition, so that she had venomously opposed Kick’s love match to Billy, as well as her ‘engagement’ to the still-married Peter Fitzwilliam.

As for Joe Snr, Leaming claims that Lady Jean Ogilvy (Jean Lloyd) told her something ‘many years later’. Though Lady Jean’s parents, the Airlies,

might have encountered Robert [Worth] Bingham [Joe Kennedy’s precursor, the Kentuckian whose own daughter, Henrietta, had affairs with both the gentlemen and the ladies of the Bloomsbury Group] socially even if he had not been the American ambassador in London, they almost certainly would never otherwise have met Joe Kennedy, who was of a lower social class than his predecessor and was — to Jean’s sense — possessed of a personal ‘coarseness’ that seemed highly unusual in a diplomat.

Leaming says that Joe Kennedy sought the London post to avenge some of the social slights he’d suffered at home, and ‘to elevate himself and his family socially’.

There is more than a difference in tone between Leaming and Byrne. According to Leaming, on the occasion of a crucial visit to Hatfield in June 1938, when she got to know several of the Cecil clan, Kick felt bullied and harassed by Robert (later to become the 6th Marquess of Salisbury, the son of Bobbety, the politician) Cecil’s practical jokes — an apple-pie bed and the theft of all her left shoes. Byrne, on the other hand, thinks this was a triumph for Kick, who appeared for dinner in two right shoes, one black, the other white, nicely complementing her black-and-white dress. How-ever, both cite the same source, Kick’s diary for 17 June. Leaming says Kick got help putting the bed right from Anthony (Lord) Loughborough, while Byrne says ‘Anthony Eden helped her to straighten out the sheets’; and both say the shoe prank was, a little chillingly, the idea of Robert’s grandmother Alice Salisbury.

The cover of Byrne’s book reads Kick: The True Story of Kick Kennedy, JFK’s Forgotten Sister and the Heir to Chatsworth. Byrne (whose husband is the provost of Worcester College, Oxford) has an essential Oxford comma missing in the subtitle. More puzzling is Leaming’s sentence (about Andrew Cavendish, the future Duke of Devonshire): ‘A year earlier he had begun to insinuate himself at parties to which his older brother had been invited.’  She begins her book with the late Andrew Devonshire, then an arthritic 82-year-old, confiding to her about Kick, with startling familiarity, that ‘I fancied her. I wanted to claim her for myself.’ Andrew’s learning of his brother Billy’s sudden passion for Kick, says Leaming, meant ‘a lifetime of fraught personal relations’. She compares this relationship, soured by primogeniture, to that of the Kennedys Joe Jnr and Jack, untouched by the expectations dependant upon birth-order; and promptly contradicts herself by calling the elder, Joe Jnr, the ‘anointed’.

The red-top prose in which she relates her racy stories is belied by the ample notes at the back, most of which credit ‘author interview’ — but without ever giving the date on which the delicate conversations took place. The apparatus seems misleading — as, I imagine, are the juiciest stories. ‘By Kick’s own account to both Fiona Gore and Jean Lloyd, the wedding night proved to be a disaster and a disappointment, mainly, she insisted, because of Billy’s inexperience,’ writes Leaming; though, ‘as Kick later confided to both of them, “Billy finally… figured out how to do it”.’ Catholic Kick was certainly a virgin. And it seems surprising, that a young man of Billy Hartington’s class and era would have suffered from inexperience. He would surely have known the addresses of some of the ladies of Half Moon Street.