It's a special day for LeBron James -- not only is it his firstborn son's birthday -- Bronny Jr.turned 18 years old!!
The Lakers superstar went to Instagram to post a bday tribute on Thursday, using a throwback photo of him and Bronny during his first stint with the Cleveland Cavaliers ... along with a photo of father and son during their recent visit to Ohio State.
"How is this kid 18 years old today y'all!!??!!" James said in the caption, "I can't deal with it.