Harry and Meghan's interview with Oprah Winfrey won't be delayed while Prince Philip is in hospital

Watch: Prince Philip has had 'successful procedure' for pre-existing heart condition

Prince Harry and Meghan Markle's interview with Oprah Winfrey won't be delayed while his grandfather, Prince Philip, is in hospital, a source has said.

There have been calls for a delay to what is expected to be a "landmark" interview between the royal couple and the US talk show host because the Duke of Edinburgh is still in hospital - his longest stay ever.

The 99-year-old went in more than two weeks ago for treatment for an infection, but has since been transferred to a specialist cardiac hospital and had a procedure on a pre-existing heart condition.

He is going to be in St Bartholomew's for a number of days while he recovers from the procedure, and so is likely to still be there when the show airs on Sunday night in the US.

A source close to the Duke and Duchess of Sussex told the PA news agency: “There are a lot of people who are going to talk about this until the programme airs, but the programming and all the rest of it is ultimately up to CBS, we’re not involved in that side of things.

“As it stands, I don’t think there is any intention from the programme maker to change its air date.”

Watch: Meghan accuses Royal Family of 'perpetuating falsehoods'

Read more: Should Harry and Meghan's Oprah interview air while Prince Philip is in hospital?

The two hour show is going to premiere in the US on 7 March, and then will be shown in the UK on 8 March, with ITV airing it at 9pm.

Penny Junor, author of Prince Harry, Brother, Soldier, Son, told The Daily Beast the interview could look inappropriate.

She said: “Anything could hijack this interview. Philip is ill. He is 99 and could die at any time. They were not to know he would get ill, but it could be seen to be the wrong time. But I doubt it is in their gift to postpone the interview. The control is in the hands of CBS and Oprah.”

Victoria Murphy, royal author, told BBC News: "This interview is a landmark moment, it’s an opportunity for them to have their say.

"The test of this will be whether people in the middle ground who don’t know what to believe, whether the Sussexes will be able to provide that information [to convince them]."

Previously, Joe Little, managing editor of Majesty magazine, told The Telegraph there is "unease" about the timing of the interview with the Duke of Edinburgh now in a second hospital.

He said: "This interview has been hyped significantly by CBS and the ball is very much in their court. The transmission date is likely to be set in stone and I can’t imagine it being pulled."

Meghan referred to 'The Firm' as she sat down to talk to Oprah about life in the royal family. (CBS)
Meghan referred to 'The Firm' as she sat down to talk to Oprah about life in the royal family. (CBS)

Read more: How can I watch Harry and Meghan's Oprah interview in the UK?

The programme has been extended from its original 90-minute time slot to two hours, with a new clip released overnight on Thursday.

The clip shows Meghan explaining that she didn't know how "The Firm" could expect them not to address anything when they were "perpetuating falsehoods" about her and her husband.

Previous trailers for the programme showed Winfrey stating that nothing had been "off-limits" during their chat, as Harry shared his fears of "history repeating itself" as they decided to step back from senior royal life.

Oprah with Meghan and Harry airs on ITV at 9pm on 8 March in the UK.

Watch: Prince Harry opens up about Princess Diana’s death in exclusive interview with Oprah