TMZ Sports has learned ... the Tennessee Titans star RB wanted to turn all of his pigskin accomplishments -- starting from high school -- into some bling for his 28th birthday this week.

So, he hit up celebrity jeweler Ali The Ice Champ in Dallas ... and the dude delivered the amazing piece in time for Henry's cake day this week.

The bling is awesome -- it features a huge 6.5-inch "Y" pendant that represents Henry's days at Yulee High School in Florida. The pendant also features a little VS1 diamond-infused Heisman Trophy to immortalize the award that Henry won back in 2015.

On the chain, Ali tied together logos of the Yulee Hornets, Alabama Crimson Tide and Tennessee Titans ... and then he added several beads to represent some of Henry's historical football moments.

We're told some of those feature a diamond 12K bead for his 12,124 rushing yards in high school that set a national record as well as a diamond 2K bead for his 2,000 rushing yards in the Titans' 2020 season.

Ali -- whose clients range from Ezekiel Elliott to Post Malone -- tells us that Henry's one-of-a-kind necklace carries 100 carats of VS1 E-F color diamonds and has over half a kilo of gold.

No word on what it all cost the King ... but Henry's made over $30 million in his NFL career, so he's certainly got the cash to spoil himself.