Asked about Prince William's engagement to Kate Middleton, the long-haired comedian claimed the couple were merely swapping pricey jewellery before consummating their marriage.
'The aristocracy are planning to clatter their genitals at each other, but first they swap expensive jewels,' he said. 'It is a custom. Then there will be a new king.'
Brand, 35, made the lewd remarks during an appearance on Conan O'Brien's US chat show.
The Forgetting Sarah Marshall star said he did not know what to make of Prince William's impending nuptials because he had mixed views about the monarchy.
'I think that's quite nice to have a monarchy – because I like those shiny hats they wear,' he said. 'I also enjoy elaborate furniture – thrones and what not.
'But hierarchical structures, which accentuate privilege and oppress people, I'm not so into. But then when I do meet royals, I get all giddy.'
Brand was not, however, quite so hesitant when it came to discussing his own marriage to Katy Perry and flaunting his sparkling wedding ring.
'It's rather elaborate because I was wed in India and there was an element of glamour to the proceedings,' he said.
'Plus, I'm a bit of a magpie – I'm attracted by sparkly things.'