How do JavaScript instances access private methods without prototype inheritance?

My understanding is that private methods are not part of the prototype chain, and therefore, are not inherited by subclasses. However, I am confused about how instances of a class access private methods when those methods are invoked through public methods of the class.

class MyClass {
  #privateMethod() {
    return 'I am a private method';
  }

  publicMethod() {
    return this.#privateMethod(); // Access private method from within the class
  }
}

const instance = new MyClass();
console.log(instance.publicMethod()); // Logs: I am a private method

When instance.publicMethod() is called, this inside publicMethod refers to instance. Since private methods are not part of the instance itself or the prototype chain, how does this.#privateMethod() work? How does the private method get accessed even though the instance doesn’t directly contain the private method?