How to initialize a const string as the concatenation of two strings during compilation time?

The following code initializes two const strings during compilation time:

class Test
{
public:
    static constexpr const char* LOS = "Los ";
    static constexpr const char* ANGELES = "Angeles";
};

How to create another constant string (const char* or const std::string) as the concatenation of the two constant strings? Adding the following line

static constexpr const std::string LOS_ANGELES = std::string(LOS).append(ANGELES);

emits the error:

error: the type ‘const string {aka const std::basic_string<char>}’ of constexpr variable ‘Test::LOS_ANGELES’ is not literal