How to count distinct values in a column of a pandas group by object?

I have a pandas data frame and group it by two columns (for example col1 and col2). For fixed values of col1 and col2 (i.e. for a group) I can have several different values in the col3. I would like to count the number of distinct values from the third columns. For example, If I have this as my input: 1 1 1 1 1 1 1 1 2 1 2 3 1 2 3 1 2 3 2 1 1 2 1 2 2 1 3 2 2 3 2 2 3 2 2 3 I would like to have this

[somemo]

“.apply(lambda x: len(x.unique()))”