A lone man in uniform knelt at the grave of Beau Biden in Delaware on Wednesday — as Joe Biden was being sworn in as the 46th president.

The unidentified mourner, who appears to be wearing a police uniform, was snapped on one knee with his head bowed before the grave, a photograph posted on Twitter shows.

“Poignant moment,” the caption reads. “While Joe Biden gave his inauguration speech, a lone man in uniform knelt at the Delaware grave of his son Beau.”

During a pre-inauguration speech Tuesday, Joe Biden teared up as he honored his late son, who died of cancer in 2015 at the age of 46.

“Ladies and gentlemen, I only have one regret,” said Biden, 78. “He’s not here, because we should be introducing him as president.”