Clark Gable -- Frankly, My Dear ... I'm a Great Grandfather!

Clark Gable passed away 54 years ago, but his name lives on ... in the form of his first great grandchild.

Gable family sources tell TMZ ... Gable's granddaughter Kayley (who appeared on the reality show "Paris Hilton's My New BFF") gave birth New Year's Day to a baby boy.

The name? Ocean Clark Gable.

We're told Ocean was born three weeks early -- but still clocked in at 7 pounds 6 ounces -- and the tube is to help him get a little extra oxygen.

Ocean had a 4-day stint in the hospital, but he's home and doing well.