Mel Gibson had a busy last few days -- not only pleading no contest to misdemeanor battery, but becoming a grandfather for the third time ... TMZ has learned.


Sources close to Gibson tell TMZ his daughter Hannah gave birth Saturday night to a baby boy. It's Mel's third grandchild -- two boys and one girl -- all from Hannah and her hubby, blues singer and guitarist Kenny Wayne Shepherd.

We're told Mel hit up his church in Malibu yesterday (see above) -- but ducked out early to spend time with the new baby, who has yet to be named.