FIRST LOOK! Photos of Blake Lively and Leonardo DiCaprio holding hands on moonlight walk!

So there it is, ladies and gentlemen! Proof of what we’ve known for weeks now, Blake Lively and Leonardo DiCaprio ARE DATING!

After weeks of speculation and high-profile partying up and down the French Riviera, DiCaprio, 36, and Lively, 23, were photographed holding hands during a romantic, moonlit stroll after dinner in Monte Carlo May 27– and only Us Weekly has the exclusive photos.

“He looked very in love,” a witness says in the new issue, on stands Wednesday. Two days later, the Oscar-nominated actor — who has been wining and dining the Gossip Girl star for weeks over dinner, helicopter and yacht rides and glitzy A-list bashes — brought her as his guest at a Grand Prix-viewing bash aboard a yacht.

“Her face lit up when Leo was talking,” a fellow reveler says.

“He had introduced Blake as his girlfriend,” adds a source. “I would say they’re totally smitten!”

Although DiCaprio and model Bar Rafaeli called it quits just a few weeks ago, he and Lively first connected at an NYC business meeting back in November — and shared a kiss at a Hollywood bash in January.

“I’ve never seen him like this with a girl,” adds the insider of DiCaprio.

She seems so young, doesn’t she? 13 year age difference is pretty big, if you ask me! I know it’s not too bad, in Hollywood’s eye – but the life difference between 23 and 36 has to be huge.

Oh well, life’s short – might as well go for it!

For much more on this suddenly hot-and-heavy romance — how DiCaprio has spared no expense for his new lady, Lively’s decade-long crush on the star, and more exclusive photos of their PDAs in Europe — pick up the new Us Weekly, on stands Wednesday!