Twenty-five years after he was supposed to have graduated from high school, BILLY JOEL received his diploma this week at Hicksville High School on Long Island.

The 43-year-old singer and songwriter didn't graduate with his class in 1967 because, as RICHARD HOGAN, the school's principal explained yesterday, "he was missing one credit in English." He was working as a musician and overslept, missing an English exam, said Mr. Hogan, who was Mr. Joel's fifth-grade gym teacher.

But the Piano Man wasn't let off the hook: the school asked him to send in samples of work that might fill the missing requirements. "He submitted some of his actual works, and we said, 'My gosh, this more than satisfies,' " Mr. Hogan said.

So on Wednesday evening, Mr. Joel put on a gown -- no cap, though -- and marched with the 305 members of the class of '92. After the valedictorian and salutatorian had their say, he addressed the class:

"Well, here I am, Mom. I'm actually going to get my high school diploma, and it's only 25 years after everyone else got theirs. But Mom, don't worry. I can finally pull myself out of this dead-end job I have and start working on a career with a real future."