Christie Brinkley's Ex Peter Cook Gets Engaged to 21-Year-Old Student

Christie Brinkley's ex-husband, Peter Cook, popped the question to another blonde bombshell ... but this one's just old enough to legally pop a cork.

Peter is now engaged to tie the knot with 21-year-old Alba Jancou. He dropped down to one knee and proposed to the college hottie last month outside a church in Santorini ... according to the NY Post.

Peter's been hanging out with Alba since at least this summer, showing her off at some fancy parties in the Hamptons. We know -- age is just a number, but this is kinda wild.

Peter and Christie's daughter, model Sailor Brinkley-Cook, is the same age as Alba ... her new stepmom-to-be.

Alba is currently a student at Tulane University in New Orleans, and according to her social media, she'll be graduating in 2021. As for the other important date in her life -- no word on when the happy couple's planning to walk down the aisle.

BTW ... the age gap is the same as Dennis Quaid and his fiancee, Laura Savoie, who got engaged earlier this month in Hawaii.