WASHINGTON — A sweet “promposal” from a teen to his grandmother turned sour after his high school barred her from attending.

Alabama high school senior Bryce Maine asked his grandmother to prom in celebration of his 18th birthday. In classic promposal fashion, Maine surprised her with a “PROM?” sign, later posted on social media, generating a few “aww’s” and “likes” on the internet.

“My Grandma is the most important woman in my life, and she’s never had a prom before so I figured why not let her go with me,” Maine told “Inside Edition.”

Maine’s grandma, Catherine, said yes, and even bought a new dress for the event.

The teen’s promposal went viral a few days later after the his school, Eufaula High, said grandma wasn’t allowed to attend.

“Attendees must be under the age of 20 and/or should be enrolled at EHS,” the school said in a statement.

“For the 10 years I have been high school principal, we have denied requests each year from students asking to bring older dates to prom. We do not chance leaving any stone unturned when it comes to safety,” the school principal added to the statement, according to WTVM.

Since the school’s decision, #letnannygotoprom has generated support online. Eufaula High School’s prom is set for Saturday, April 8.