Marginal Cost at Minimum Average Total Cost

In the context of microeconomics, consider a firm that is evaluating its cost structure. The firm has both fixed and variable costs associated with production. Fixed costs remain constant regardless of the output level, while variable costs vary with the level of production. If the firm decides to operate at a level of output where average total cost (ATC) is minimized, what is true about the marginal cost (MC) at this output level?