Prince Harry is reportedly isolating in the US in preparation for an emergency trip to see his ailing grandfather Prince Philip.

Harry is said to be preparing to fly to the UK in a bid to see his 99-year-old grandfather, the Duke of Edinburgh, who is being treated for a mystery illness in hospital.

British tabloid The Mirror reports Harry is self-isolating in his Californian mansion so he can fly to Britain at a moment’s notice if his condition worsens.

Harry is reportedly getting frequent updates on his grandfather’s condition and has already made plans to fly on a private jet.

As in Western Australia, visitors from the US must isolate in hotel quarantine upon arrival to the UK.

Harry will need to undergo a COVID test to enter the UK.

Prince Philip is expected to spend a third night in a London hospital for “observation and rest” after being admitted earlier this week after feeling unwell.