if you say that someone is one in a million, you mean that they are very special because they have such good qualities.
She's the sweetest, most generous person I know - she's one in a million.
be one in a million
To be regarded as very rare and excellent or spectacular. Your new boyfriend is one in a million. I can't believe he spent the weekend with your entire family and actually enjoyed himself.This opportunity is one in a million—you have to take it!