Solving a diophantine equation involing squares and a prime number

Question

I have the following diophantine equation

I wish to find and prove that there is ONLY ONE solution to the following equation

$x^2=y^2 + 31$

I understand that 31 is a prime number thus we can equate

$x^2 - y^2$ is a perfect square therefore we can write

$(x-y)* (x+y) = 31$

However I am lost as to what to do after this part.