James Murray, son of the Earl of Mansfield, sent his teenage lover 21 text messages begging her forgiveness after she accused him of rape, a court heard.
Murray, 42, denies raping the teenager in June 2011 after allegedly "spiking her Ribena".
Following the alleged attack, after which the girl claims she awoke on an inflatable bed with her tracksuit trousers around her knees, the defendant urged her to take a morning-after pill because a condom had split, an Oxford crown court jury heard.
A string of text messages was shown to the court. In them, Murray, who was working as a computer engineer in Oxford, asked the girl whether she would contact the police.
He told her not to "freak out" and added that the pill was "just a precaution".
Eton-educated Murray, who grew up at his family's ancestral home, Scone Palace in Perthshire, Scotland, and gave his address as Logiealmond, claimed the pair were in a consensual relationship for 10 days. During that period they slept together six times, he said.
The two met when the girl, now 17, was just 15, and formed a friendship after she turned 16 and regularly began to visit his Oxford flat to watch television and play computer games.
"I'm really sorry, I know you blame me, if you call the police and cry rape and that I spiked your Ribena then our friendship is over because I can't cope with this stuff," one message read.
Nicholas Syfret QC, defending, suggested that the girl, who appeared by video link, made up the story, which had since spiralled out of control.
The trial continues.