Media playback is unsupported on your device Media caption Prince Harry: "It's been a big learning curve"

Prince Harry says he will go on using his position to "shine a spotlight" on issues close to his heart.

He was speaking as he guest edited BBC Radio 4's Today programme, which focused on the armed forces, mental health, youth crime and climate change.

He interviewed former US president Barack Obama and his own father, Prince Charles, as part of the radio show.

He also said his fiancee Meghan Markle had enjoyed spending Christmas with the family "she's never had".

Ahead of his wedding in May, Prince Harry said he was determined 2018 would be a "fantastic year".

He said: "Post-Christmas... I just hope everyone out there has had a chance to just think about the things that really matter and the difference that every single one of us can make.

"Part of my role and part of my job is to shine a spotlight on issues that need that spotlight, whether it's people, whether it's causes, issues, whatever it is.

"So I will continue to play my part in society and do my job to the best of my abilities so that I can wake up in the morning and feel energised."

In the interviews, Mr Obama said irresponsible use of social media was distorting the public's understanding of complex issues, while the Prince of Wales said climate change was causing "untold horrors" in different part of the world.

Family traditions

As the programme ended, presenters Justin Webb and Sarah Montague turned the microphone on the fifth in line to the throne, who spent Christmas at Sandringham with members of the Royal Family and his fiancée.

Media playback is unsupported on your device Media caption Prince Harry discusses Meghan Markle's first Christmas with the Royal Family

Prince Harry said he had an "amazing time" - Ms Markle "really enjoyed it and the family really loved having her there" although there were "plenty" of family traditions he needed to explain.

The 33-year-old said they had a "great time" with the Duke and Duchess of Cambridge and "running around with the kids".

American actress Ms Markle's presence at Sandringham was the first time someone yet to marry into the Royal Family has been invited to join their Christmas celebrations.

Prince Harry said: "She's done an absolutely amazing job, she's getting in there and it's the family that I suppose she's never had".

Best man offer

Meanwhile, boxer Anthony Joshua, who was a guest on the programme, tweeted a picture of himself with Prince Harry and offered to be his best man.

The world heavyweight champion wrote: "Back to work this morning! Congrats on everything this year and no pressure on the R4 guest edit! P.S. Need a best man?"

BBC royal editor Nicholas Witchell said the prince had previously expressed doubts about his public role but the programme showed that was no longer the case and he "wants to make a real difference in the work that he does".

However, he added Prince Harry was not able to ask genuinely probing questions in the interviews because, as a member of the Royal Family, he has to avoid areas that might be deemed to be political.

'Big learning curve'

It is the 14th year public figures have been in control of Today's output between Christmas and New Year.

Image copyright JEFF OVERS/BBC Image caption Prince Harry in the Today studio with presenters Justin Webb and Sarah Montague

Other guest editors include a robot, Bletchley Park code-breaker Baroness Trumpington, Tamara Rojo of the English National Ballet and poet and novelist Benjamin Okri.

Prince Harry's programme also featured an audio diary recorded in Toronto at the Invictus Games, the Paralympic-style competition for injured service personnel he launched in 2014.

And he conducted an interview with British artificial intelligence entrepreneur Demis Hassabis.

Another section saw Met Police Commissioner Cressida Dick interviewed live in the studio as Prince Harry sat in the editor's chair.

Prince Harry chose Abdurahman Sayed, from the Al-Manaar Muslim Cultural Heritage Centre in North Kensington, which has been helping people affected by June's fire at nearby Grenfell Tower, to speak in Today's Thought for the Day spot.

On his editing role, Prince Harry said: "I haven't done that many interviews but it was quite fun, especially interviewing President Obama.

"It's been a big learning curve, but also these are incredibly important topics that I think we all need to think about that need to be discussed and I'm incredibly fortunate to have a platform like this."

Harry 'bouncing towards the new year'

Image copyright Jeff Overs/BBC

By Jonny Dymond, BBC royal correspondent

One claims to speak for the nation and one claims to speak to the nation. On Radio 4's Today, the Royal Family and the BBC came together in a cosy embrace.

Few of the prince's causes were unrepresented and he was himself dotted through the programme, encouraging and enthusing about nearly everything.

He is clearly bouncing towards the new year, a time he insisted would be full of "great change - good things are going to happen in 2018".

There was little in the way of actual hard news - former US President Barack Obama has more time on his hands; the Prince of Wales - "Pa" as Harry called him - is concerned about the environment; Harry doesn't drink coffee, or much of it.

But there were glimpses of the gilded cage. A note of wistfulness in his voice when he asked Mr Obama about "stepping off the treadmill" of constant exposure.

Prince Harry, who was in the Army for 10 years, said he wanted the armed forces to feature because "there's a huge role they play and we must make sure it's not sympathy but respect we show".

Media playback is unsupported on your device Media caption Boxers or briefs? Prince Harry grills Barack Obama on his likes and dislikes

In his interview, the Prince of Wales said he had "bored you [the prince] to tears over so many years" with discussions on the environment but the public was "beginning to realise that what I was trying to say may not have been as dotty as they thought".

Prince Charles said he wanted to "ensure that you and your children, my grandchildren... have a world fit to live in, that provides them with opportunity".

Media playback is unsupported on your device Media caption Prince Charles on dealing with climate change

Mr Obama reflected on his time in office and voiced concerns about the direction of the US.

He warned social media was stopping normal conversations and talk about the responsibility of people in positions of leadership.

In one of his first interviews since leaving office, Mr Obama expressed concern about a future where facts are discarded and people only read and listen to things that reinforce their own views.

Media playback is unsupported on your device Media caption Barack Obama opens up on Today about how he felt post Donald Trump's inauguration

He also reflected on the day he handed over power to Donald Trump.

Despite feeling satisfied, he said it was "mixed with all the work that was still undone".

Listen to Prince Harry's edition of the Today programme on iPlayer