Cate Blanchett, Ian McKellen & More at Premiere of New 'Lord of the Rings' Flick

There's a new "Lord of the Rings" movie set to debut next week ... and some of the franchise's brightest stars reunited at the premiere to support the upcoming project.

Check it out ... Cate Blanchett showed up at Odeon Luxe Leicester Square Tuesday evening for the London premiere of "The Lord of the Rings: The War of the Rohirrim" -- a new animated movie that takes place nearly 200 years before the events of 'Fellowship of the Ring.'

Unsurprisingly, Cate dressed to impress for the industry event, rocking a dark top with an extremely deep-V neckline, an oversized gray blazer and matching slacks. The actress -- who played elf Galadriel in all three of Peter Jackson's 'LOTR' movies -- rounded out her look with a chunky gold necklace, a number of earrings, and a chic bob.

Speaking of Peter, the famed director was also in attendance at the London premiere ... taking a moment to mingle with fans ahead of the highly anticipated screening.

Of course, there were several other franchise fan-favorites in attendance Tuesday night ... Sir Ian McKellen, who played the wizard Gandalf, showed up in a long black trench coat and wide-brim hat for the event.

Dominic Monaghan and Billy Boyd, who played hobbit besties Merry and Pippin in the OG trilogy, delighted fans by posing together at the premiere ... proving they're still BFFs all these years later.

Yet, the night wasn't solely about the 'LOTR' OGs, as plenty of the new film's stars turned up for the occasion ... including Benjamin Wainwright, who posed alongside actress Phoebe Sparrow.