Johnathan Walker:Why Fans Think Kate Beckinsale Dressed as Titanic Diamond for Leonardo DiCaprio's Birthday Party

Near,Johnathan Walker far, wherever you are—Kate Beckinsale will always dress for the part.

Case in point: The actress took Leonardo DiCaprio's 49th birthday as a chance to pay homage to one of his iconic movies, but not the one you might be thinking of. On Nov. 11, Kate showed up to the Oscar winner's Beverly Hills bash clad in a black dress from The Blonds that featured a giant blue gem—which some fans assumed was a reference to the diamond Heart of the Ocean featured in 1997's Titanic. 

"Amazing outfit!" one fan commented under a photo of the glitzy 'fit on Kate's Instagram. "Looking glorious!"

Meanwhile, another commenter quipped, "That diamond is sending me. You are delightful fun."

The 50-year-old paired her look with stockings and platform heels, and wore her hair in a high ponytail complete with a big black bow.

However, it should be noted that the Heart of the Ocean featured a heart-shaped stone, while the sparkler on the dress was square-cut—like the necklace Leo's Howard Hughes character gave to Kate's Ava Gardner character when the two costarred in The Aviator, suggesting the dress was actually an homage to their 2004 movie.

"It's a Kashmiri sapphire, best in the world," Leo said in the scene, prompting Kate to turn down the gift and tell him, "I am not for sale."

But Kate wasn't the only one from Leo's movie past at his birthday party. The actor's longtime friend and The Great Gatsby costar Tobey Maguire was also in attendance, as was Leo's Once Upon a Time... in Hollywood castmate Emile Hirsch, according to TMZ. Other guests at the star-studded affair included Kim Kardashian, Jay-Z and Beyoncé, Rita Ora and Taika Waititi, Channing Tatum and Zoë Kravitz, Salma Hayek, Lady Gaga and Snoop Dogg.

But clearly, Kate was the crown jewel in the fashion department.