Emotional day for Aaron Carter's family ... with his son visiting the late singer's grave site, exactly one year after his death.

Sunday marked the first anniversary of Aaron's passing, and his fam stopped by his headstone at Forest Lawn Hollywood Hills.

Aaron's ex-fiancée Melanie Martin brought their son Prince with her ... and folks who were there tell us Aaron's twin sister, Angel, was already at the gravesite when Melanie and Prince arrived.

In addition to Aaron's mourning family, we're told fans also showed up to pay their respects ... many leaving candles and flowers.

TMZ broke the story ... Aaron was found dead in his Lancaster, CA home Nov. 5, 2022, and the official cause of death was drowning as a result of being under the influence.

On Aaron's death anniversary, we're told Prince walked up to his father's gravestone and counted all the candles left by fans -- there were 20 -- and Melanie hung around until the cemetery closed for a private moment at Aaron's grave.