Jackie Kennedy 'had four-year affair with Bobby Kennedy'

The former first lady was so in love with Mr Kennedy, that when he was shot during his presidential campaign in 1968 it was her - not his wife Ethel - who instructed doctors to turn off his life support machine.

Ethel was aware of the affair but chose to ignore it, according to Bobby and Jackie: A Love Story, by C.David Heymann.

Several political insiders and celebrities are quoted in the book, which will be published in the US next week.