Army Reservist Harland Fletcher walks on stage to receive his high school diploma during a ceremony Monday.

BRENTWOOD, Calif. — A California high school principal on Monday issued a public apology and handed a diploma to an Army Reservist who was not allowed to wear his military uniform at his graduation ceremony last week.

Liberty High School Principal Patrick Walsh apologized to Harland Fletcher, a private first class reservist in the U.S. Army, and took full responsibility for the mishap at a ceremony where many waved American flags. Fletcher sat out the Friday ceremony at Liberty High School after the principal told him he would have to wear a cap and gown over his uniform if he wanted to participate.

“I made a mistake last Friday night, and I don’t mince words. I deeply regret what occurred,” Walsh said.

Walsh held a private ceremony at the high school in Brentwood, Calif., that was attended by Fletcher’s family and about 100 people, many of them veterans in uniform who came out in support.

Fletcher said he wants to send a message that the military shouldn’t be disrespected and that servicemen stand together.

The 18-year-old high school graduate said he did not want to make the ceremony about him, but rather highlight what the military is about.

“I didn’t really need the apology, but I wanted to send a message that the military is about friendship — brothers and sisters standing together, not just letting someone trample over us,” Fletcher said.