The Lion King cast were given these rules when meeting Harry and Meghan

The celebs were out in force earlier this week at The Lion King UK premiere in London, and everyone from Beyoncé to the Prince Harry and Meghan Markle were on the red carpet.

But when you're meeting royalty there are certain guidelines given to you, and during an interview actors Seth Rogan and Billy Eichner opened up about the strict rules they had to follow when meeting the Duke and Duchess of Sussex.

'They give you a list of things you're supposed to do when you meet them, all this protocol,' Billy, who voices Timon, told Heart Radio.

'It all sounds very formal and very old-fashioned and very official, and we didn't know if people actually do it or not ... plus, we're not from this country.'

The pair elaborated during an appearance on This Morning, with Billy saying: 'They tell you you're meant to say Your Royal Highness, you can't speak until your hands are locked together in a handshake, and all of these crazy things.'

Seth, who voices Pumbaa, added: '[It was] "A) respect their personal space" ... They're the only people I've met that come with protocol, so that was interesting.

'We were like, "Do you really say Your Royal Highness? Are other people saying that?" In my head I kept thinking, "Or else what? How does this go wrong?"'

Luckily, everything went to plan - apart from the fact that their co-star, Keegan Michael Kay, shook Harry's hand without addressing him formally.

Seth joked: 'Not saying anything — that wasn't on the table.'

Oops.