ET breaks news that JACK BLACK and his wife TANYA have welcomed their second son.

Jack told our THEA ANDREWS at the Los Angeles premiere of 'Kung Fu Panda' that the baby was born about a week ago.

Papa Jack, who told us he's been changing a lot of diapers over the past week, described little Jack as "fresh out of the oven." The newborn joined big brother, SAMUEL, almost 2. Jack and Tanya married in 2006.

Other stars opening up to Thea on the red carpet at the premiere included DUSTIN HOFFMAN and LUCY LIU.

Debuting in theaters on June 6, 'Kung Fu Panda' is the animated story of Po, a panda who works in his family's noodle shop, but is a big fan of kung fu. When Po gets the opportunity to train with the Furious Five -- the best martial arts experts in the world -- it isn't long until Po has to use his new skills to fight his enemies.