Don McLean says don't let big diamonds fool you ... he's not engaged to a smokin' hot, much younger babe ... hmmmm.
Paris Dylan is NOT his fiancee ... so says Don's rep, who adds the relationship is strictly professional.
The 22-year-old model's been blowing up her page with pics of her and Don together for the holidays, with captions like "Aloha & Merry Christmas from my Donny and I" ... all while wearing a fat rock on her ring finger.
Paris does Don's social media. You'll recall his wife filed for divorce earlier this year.
So bye bye, Paris. No Mrs. American Pie here ... so they say.