The overtone produced by a string vibrating at its fundamental frequency of 528 Hz will be its first harmonic.

Here's why:

* Fundamental Frequency: This is the lowest frequency at which a string can vibrate. It's also known as the first harmonic.

* Overtones: These are frequencies higher than the fundamental frequency that are also produced by the vibrating string.

* Harmonics: Harmonics are overtones that are whole-number multiples of the fundamental frequency.

Therefore, the overtone produced in this case is the first harmonic, which is simply the fundamental frequency itself (528 Hz).

The next overtones would be the second harmonic (2 * 528 Hz = 1056 Hz), the third harmonic (3 * 528 Hz = 1584 Hz), and so on.