Prosecutors said he raped Louise in an “act of spite” during the attack in the Hunt family home in Bushey, Hertfordshire, on 9 July last year after she broke up with him 13 days earlier.
Clifford, who refused to attend the four-day trial at Cambridge Crown Court, claimed DNA evidence found on her body was from a consensual sexual encounter 16 days before the attack.
But he was found guilty by a jury after the court heard his explanation was “completely untenable”.
Kyle Clifford, 26, previously admitted murdering BBC racing commentator John Hunt’s wife Carol Hunt, 61, and their daughters Louise, 25, and Hannah, 28.
He also pleaded guilty to false imprisonment of Louise, who was tied and gagged with duct tape, and possession of the crossbow used to kill her and her sister, and the 10-inch butcher’s knife he stabbed their mother to death with.
