This statement is not true.
If a number is whole number, it will not always be a natural number. An example of a whole number that is not a natural number is 0. Think of natural numbers as counting number so 1, 2, 3, 4, ... and so on. Whole numbers are natural numbers but they also include 0. When we count up, we usually don’t starts with 0 so it’s not a natural number but it is a whole number.
Therefore, if a number is a whole number, it does not necessarily have to be a natural number.