The letters show Laurie Lee had feelings for Molly Smart.
Personal letters, written by Gloucestershire author Laurie Lee, which have been sold at auction, reveal for the first time he was at the centre of a 'love triangle'.
The collection, penned by the writer of Cider with Rosie, fetched £1500 in the sale on Monday.
It was already known that Laurie Lee had been romantically involved with Betty Smart from Gloucester when he was a teenager growing up in Slad.
But the letters show he also had feelings for her older sister Molly.
Rose Sanguinetti, from auctioneers Lawrences of Crewkerne, explained:
"The first letter begins - 'Damn, no. I can think of nothing more miserable than a polite acquaintance pact'.
"So maybe she's not so keen on taking it a step further.
"But I think it's all fairly young and innocent.
Later letters show the pair remained friends.
"The last letters in the series relate to him sending birthday wishes to her son," added Rose.
"This was some years later after she'd married so they were obviously friends for many years.
"He's obviously a very important author of the 20th century and there's still interest in his life and work."
Laurie Lee died in 1997. He is buried in Slad churchyard.