Sophie has now taken to Twitter to clarify that she is not engaged to Benedict – that person is actress and director Sophie Hunter.
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Sophie Turner has clarified she is not marrying Benedict Cumberbatch
"Thanks to everyone who is congratulating me, but it's another Sophie who is marrying Benedict Cumberbatch," the 18-year-old wrote. "Nice one guys haha."
News of Benedict's engagement was revealed this week with a discreet and formal announcement in The Times newspaper.
"Mr B. T. Cumberbatch and Miss S. I. Hunter. The engagement is announced between Benedict, son of Wanda and Timothy Cumberbatch of London and Sophie, daughter of Katharine Hunter of Edinburgh and Charles Hunter," it read.
It is thought that Benedict, 38, and Oxford-graduate Sophie started dating earlier this year, although they have been friends for many years after meeting on the set of the 2009 film Burlesque Tales.
Benedict Cumberbatch with his future wife Sophie Hunter
Sightings of the couple are very rare – one of the only times they have been seen together was when they attended the French Open in June.
Following the engagement announcement, Sophie’s family spoke of their joy.
"We are very happy for them," Sophie's mother Katharine said from her home in Edinburgh. "It's really a fabulous day. It's only just been announced so we don't know any more but it's lovely news."
Sophie's younger brother Patrick, 30, added, "We are all very happy for Soph – it's really exciting."