Daniel Williams was a “supportive and positive” soul who was celebrating his 14th anniversary on the day he died in a plane crash in San Diego … this according to his fiancée.

Hannah Ray, longtime partner of The Devil Wears Prada Drummer, shared a loving message on Instagram about Daniel … telling her followers that her life has fallen into shambles — adding she can’t imagine never seeing or touching Daniel again.

She calls Williams her best friend, partner and biggest fan … adding they had the kind of love you may only find once in a lifetime.

She finishes off her message by saying she’ll miss Daniel every day … adding she will “will do my best to be the best I can for [him] every day still.”

We broke the story … Larry Williams — Daniel’s father — told us he was among the victims in the plane crash that occurred early Thursday morning in a residential neighborhood of U.S. Navy-owned housing. The crash led to a residential  fire which injured several people and destroyed one home.