The final Dennis issue of Test Drive, which launched in 2004, goes on sale this week, with Haymarket set to take over its subscription database and close the magazine's website.
Test Drive originally had a circulation of around 114,000 copies when it first launched, but that has since been halved to 50,113.
Kevin Costello, Haymarket Magazines managing director, said: "Test Drive has been a worthy adversary over the past 18 months and we have worked hard to maintain What Car?'s position as the car buyer's number one.
"We will be taking a close look at Test Drive's content as we develop our products in the future."
James Tye, chief executive of Dennis Publishing, said the car buyer's magazine market remained an extremely tough sector and admitted, "it was very hard to see how the magazine could grow in the current advertising and copy sales climate".
"With a heavy heart we decided that the decision to sell was the best one," he said.
Despite the imminent demise of Test Drive, the car magazine sector continues to flourish, with Emap Automotive announcing plans to reinvent its leading motoring title Car.
Car said it would now be printed in a new 'square format' and would be more feature-driven as well as having a greater online presence.
What Car? has a circulation of 122,532. Haymarket also publishes Brand Repubilc.
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