Jim’s 22-year-old daughter, Jane, gave birth yesterday to a 7lb 11oz baby boy, whom she’s named Jackson Riley. Jane is a musician and married to Alex Santana, singer from the rock band Blood Money.  

Jim is a very 21st century grandpa, posting a message and picture of his new grandson on Twitter. “Jackson Riley Santana, My Grandson, Born today! This is what 7lbs 11oz of California dynamite looks like!” he tweeted proudly.

While Jim is clearly delighted with his new grandfatherly role, his 37-year-old girlfriend and former Playboy model Jenny McCarthy is putting on a brave face about being an honorary granny. “I think I am going to rock as the grandma,” she enthused a couple of months ago.

How would you feel about being a granny so young? Let us know…