Subplot Coordinates

Suppose you have created a 3x3 subplot on matplotlib using the following code snippet:

import matplotlib.pyplot as plt
fig, ax = plt.subplots(3, 3, figsize = (20, 10))

Now you want to draw a plot on the 9th cell, i.e., right bottom cell of the 3x3 subplot matrix. Which command will help you to correctly plot the same on the aforesaid cell?