Calculating Variance of Variance Estimator for Normal Distribution

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Does anyone know how to calculate the variance of the variance estimator of normal distribution?

x_i, i\in\{1,2,...,n\} are n samples of normal distribtuion N(\mu, \sigma^2).

And S^2 = \frac{n}{n-1} \sum_i (x_i - \bar x)^2 is the variance estimator, where
\bar x = \frac{1}{n} \sum_i x_i.

The question is how to calculate the following variance:
<br /> E[(S^2- \sigma^2)^2]<br />
Where the expectation is respect to sample x_i.Thanks a lot!
 
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I am pretty sure that one can find this explained in an intermediate probability textbook like Mood, Graybill & Boes.
 
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