American University graduates are marching across the stage to get their diplomas ...and to start a new chapter in their lives.

Little did Sarah Cooper know how drastically her life was about to change!

As she got her diploma, her boyfriend Sam got down on bended knee.

He says as their relationship in college grew serious, both families urged them to wait until graduation to get married.

Sam Miller says he couldn't wait another minute for her to be his fiancé'.

So he presented the ring yesterday, as soon as she had her diploma in her hand.

No word on when the happy couple will get hitched.