William's pregnant wife, Kate, was missing from the prince's arm - she cancelled her appearance at the premiere due to acute morning sickness.
McKellen, who plays the wizard Gandalf in the adaptation of J R R Tolkien's work, told reporters that it "feels proper" to celebrate the film in London, given that a large part of the cast is British and Tolkien was an English writer. Blanchett, who plays elf queen Galadriel, said it was great to see so many fans turn out considering the cold weather was "enough to drive anyone away".
The Hobbit: An Unexpected Journey which opened on Friday, is the first instalment in a prequel trilogy to director Peter Jackson's Lord of the Rings movies.
For stars like Blanchett, it was a chance to go there and back again to visit old friends more than just revisiting the blockbusters that grossed $3 billion worldwide at the box office.
"There's not a shred of cynicism that's gone into the weaving of this Tolkien tapestry," the Australian actress said.
"It's just craft and passion and I think that's what you feel from the armour down to the cinematographer through the production and to all of the actors. James said it, it's more than just a job."
In picture: (From left) Andy Serkis, Peter Jackson, James Nesbitt, Martin Freeman, Cate Blanchett, Richard Armitage and Ian McKellen
Text and images: AP