Logan and Nina were spotted kissing and hugging this week on their hotel balcony in Portofino, Italy, and it was hard to miss the huge diamond ring on her finger.

As you can see, the emerald-cut diamond looks MASSIVE, and pretty sparkly too -- no wonder Nina was wearing shades.

The newly engaged couple looks super happy here ... lounging in robes and packing on the PDA. Now, that's amore!

As we reported, Logan popped the question Sunday at Italy's famed Lake Como.

The social media and WWE superstar started dating the supermodel last May, so the engagement comes a little over a year into their relationship.

TMZ broke the story ... Logan and Nina celebrated their engagement Monday with a boat day on Lake Como, smooching and working on their tans.

We didn't see the ring during the boat trip, which is pretty remarkable, given the size ... but now it's making a big splash.