In the final episode of this series of Sherlock, the detective followed his nemesis to an incredible villain's lair, Appledore. Viewers glimpsed this impossibly futuristic mansion and assumed it was an elaborate set.
In fact it's home to one of the country's leading engineers.
In the programme, Appledore was home to Charles Augustus Magnussen, where the greatest secrets of the country's most important people were tucked away in top-secret files. The gleaming high-tech, ten-floor mansion, with its huge glass roof and viewing tower, fitted the bill precisely.
However, in real life the Daily Express reported that it's called Swinhay House, and it's home to Sir David McMurty, who runs a high-tech engineering company. He built it in the rural landscape of the south Cotswolds at a cost of £30 million.
The property was designed by Roberts Limbrick, and the company website lists some of the features as a eight bedrooms in three wings, a 25m swimming pool, an enclosed winter garden, a viewing tower, and even some more modest additions that the mega-wealthy don't normally bother with - like a bowling alley and squash court.
Does it add value?Appearing in Sherlock has raised recognition of the home and the architects, and if Sir David was to want to sell the property on, there will be plenty of the mega-wealthy who will have seen enough to whet their appetite.
There are others who cashed in on the fame of their property. Katie Price sold the home she lived in with Peter Andre in 2011, and despite the fact that she had only owned the Surrey property for three years, it was snapped up, netting a profit of £650,000. The fact that the property had featured so prominently in her reality TV shows meant that potential buyers already knew their way around.
But appearing in a TV show is not always enough to guarantee a fast sale. One of the most striking examples is a home which featured in the 'Real Housewives of New Jersey'. It went on sale in 2009 after one of the stars split from her husband. She was forced to cut the price several times to $899,000 - less than the $1.025 million she had paid for it ten years earlier.
And a Hollywood mansion which was once home to William Randolph Hearst, and was used as a set for The Godfather, went on the market in 2012 for $95 million - a significant cut from the asking price of $165 million in 2007. In the end the sellers changed their mind and put it on the rental market.