Jermaine Jackson -- MJ's Deathday Overshadows His Birthday

Jermaine Jackson says he celebrated Michael Jackson's birthday by spending time with his family and watching sentimental home videos ... but JJ explained it's also a day marked with great sadness.

Jermaine was out with his kids in Calabasas yesterday where he told us, "Today is a day to remember a wonderful human being ... but we're sobbing ... always."

Sadly, Jermaine told us the family "didn't really have birthday parties" for Michael over the years ... but says he will always cherish the memories of the two performing on stage together.