Design underlying std::condition_variable

The C++ std::condition_variable is similar to Windows' Event. While the latter is designed to be used alone, std::condition_variable must be used with std::mutex. I know about many use cases where a std::condition_variable and std::mutex combination would be perfect. I also know that in certain cases, something that can be used alone like Windows' Event would come in handy. So, I begin to wondering the design underlying std::condition_variable. Is it because std::condition_variable and std::mutex are often used together, or std::condition_variable itself uses the std::mutex to implement its functionality?