Lord Ivar Mountbatten's family name is stamped on British history. The son of the 3rd Marquess of Milford Haven, he is the great-great-great- grandson of Queen Victoria; great-nephew of Earl Mountbatten of Burma; and cousin to the Queen.

Photographs at his stately home show his place in Royal society: Lord Ivar on the balcony of Buckingham Palace, at Royal weddings and christenings, with an off-duty Queen aboard the Royal Yacht Britannia. In many of them, he is pictured with his former wife Penny by whom he has three daughters.

Yet today he has a different partner by his side, someone with handsome features, gun grey hair and twinkly hazel eyes.

Relaxed: Lord Ivar Mountbatten (left), 53, with boyfriend James Coyle outside Bridwell Park last week

At the age of 53, Ivar Mountbatten has found new love and this time it is with a man – making him the most senior aristocrat of his generation, and the first in the extended Royal Family, to come out as gay.

It is a decision which has the blessing of his ex-wife and children, his wider family and his life-long friend Prince Edward, to whose eldest child he is a godparent, as both the Earl and Countess of Wessex are to two of his daughters.

'Being a Mountbatten was never the problem,' he says, 'it was the generation into which I was born. When I was growing up, it was known as "the love that dare not speak its name", but what's amazing now is how far we have all come in terms of acceptance.

Lord Ivar with his former wife Penny by whom he has three daughters. He is the most senior aristocrat of his generation, and the first in the extended Royal Family, to come out as gay

'"Coming out" is such a funny phrase but it's what I suppose I did in a rather roundabout way, emerging to a place I'm happy to be. I have struggled with my sexuality and in some ways I still do; it has been a real journey to reach this point.'

It's a courageous declaration given the formality of his upbringing and the conventions of his class. It's not one he has made lightly and he has only been able to do it with the man he loves by his side.

His boyfriend is James Coyle, an airline cabin services director. The pair met in Swiss resort Verbier in March last year when James shouted 'Hello!' to Ivar in a bar, mistaking him for a guide with whom he had skied. It was a chance encounter but the attraction was immediate and mutual.

Aware that other media were making inquiries into their domestic life, last week he invited The Mail on Sunday to his home Bridwell Park, a Grade I listed mansion near the village of Uffculme in Devon.

It's fair to say he's sexed it up, turning it into a wedding and corporate entertainment venue with bold colours, a mix of contemporary art and old masters and a very naughty cherub on the heavily frescoed ceiling of the morning room.

'It's my sensitive side coming out,' he jokes, because actually he is happiest outside, working on his 120-acre deer estate, fencing, logging, or up a ladder cleaning out gutters.

Both Lord Ivar and James grew up in an age when to be gay was to conform to what they call 'a John Inman stereotype', something they are determined to avoid. They have a pact: no public displays of affection unless it's a hello or goodbye hug, never holding hands and no dancing together at parties. Today there are no endearments or pet names. 'Soppy? Ugh, no, not us,' says James.

Punchlines and anecdotes fall fast from them as we talk but the humour belies an experience which has been utterly life-changing. There have been some tough and lonely years.

Lord Ivar married Penny in 1994 and they settled in the Mountbattens' Elizabethan pile, Moyns Park, on the Essex-Suffolk border. He had known from his teens that he was bisexual but reveals: 'I just did not want to go there because there would have been so much grief.

'I never thought I would get married because I didn't want to be untruthful. Penny was aware before we got married. I told her I was bisexual, that my attraction went both ways. She was understanding and I will always be grateful to her. We had a lot of fun, we have three fabulous daughters and I don't regret any stage of my life.

'Ultimately, Penny did not feel sufficiently loved and she wanted more from a husband than she could get from me. Given my sexuality, I was quite surprised she married me in the first place. It was brave. Perhaps she thought she could change me but in the end she realised she couldn't.'

The couple divorced in 2011, letting it be known they had drifted apart. Ivar had a secret gay fling in 2014 but was not ready to admit his true sexuality, even to himself. That was until he met James in Verbier during après-ski drinks.

James is a year older than Lord Ivar, originally from Scotland but has lived in London for more than 30 years pursuing his career. The pair swapped telephone numbers.

It was shortly before they reconnected in London that Ivar told James the truth about his identity. He was initially shocked but now takes his boyfriend's illustrious family history in his stride, despite unexpected reminders. James, 54, says: 'For example, I called him from New York last Sunday night and he said he couldn't talk to me because he was watching the ITV series Victoria.

'Then he rang back ten minutes later to say 'my great-great-great-grandparents have just got engaged, I can speak to you now'.

'Or he'll be watching Downton Abbey and say, 'No, the under butler would never do that…' That's when I remember he's a Mountbatten.'

He continues: 'I knew there was something incredibly special about Ivar when we met, and even if we'd just gone on being friends skiing with each other and playing tennis, we'd have been glad to have that. But to have found that we both fell in love was a complete validation of all I've ever wanted.'

James comes from a more modest background, having been raised in a happy, Catholic family in Glasgow. Despite the difference in their social origins he faced the same crisis of conscience as Lord Ivar and dealt with it the same way: by leading an ostensibly heterosexual lifestyle.

He too had girlfriends throughout his 20s, not coming out fully until after the death of his mother in 2003. Since then, he has dated men but had never found a boyfriend with whom he wanted to build a life. He says: 'I was driven into the closet by not wanting to come to terms with who I was and facing friends and family in the early years. I buried it. I even had girlfriends as I tried to work out what I wanted to be.

'It was not an easy time in my teens or 20s. I'm just so pleased now to have found someone who I am happy to call my partner.

'My work involves a lot of travel. For the first time I have had someone to come home to.'

Lord Ivar's (top left) decision to come out has the blessing of his ex-wife and children, his wider family and his life-long friend Prince Edward, to whose eldest child he is a godparent, as both the Earl and Countess of Wessex are to two of his daughters

He divides his time between Bridwell Park and his flat in South-West London but hopes to spend more time in the country from next spring. Lord Ivar has been teaching him how to drive a tractor and put up deer fences and also to cook on their big bottle-green Aga.

They love to ski and cycle together and play tennis 'with a lot of deer spectating'.

It was clear soon after their first date that the relationship was a landmark in both their lives. But while James was openly gay, Lord Ivar was still in the closet and James had one non-negotiable condition: Lord Ivar had to admit his sexuality.

James says: 'If I was going to be with him, it had to be in the open with friends and family. I wanted us to be honest, not to hide anything, not to be anything else.'

Ivar agreed, even if he approached his 'coming out' with an emotional blunderbuss, never giving James more than a few minutes warning when he was about to meet Penny or the three girls, or even his older brother George, the 4th Marquess of Milford Haven, who flew in by helicopter to take the couple out for lunch.

Ivar confided first in his eldest daughter Ella, a 20-year-old graduate from Bristol University. She told him: 'Paps, it's no big deal.'

Alix, 18, found out by accident when she read Ella's diary. 'Very difficult and embarrassing,' he says, not looking embarrassed at all.

Telling Louise, then just 12, proved even more challenging.

Now James, who has no children of his own, has stepped into a parental role. Says Ivar: 'The girls like having another man in the house, it's so much easier than a potential step-mother – or step-monster. They like having James, who is just James.'

Ivar says: 'In different ways, we both struggled. Now everyone in our family knows and could not be more supportive. Neither of us wanted to have relationships which were transitory; the stereotypical view of gay relationships is that they are too fleeting, too frequent.'

Clearly this is not the case here, so I ask if they have any plans to marry, or for a civil partnership.

Ivar says: 'If you'd raised that six months or even two weeks ago, I'd have said "No way". But now it's out there [he means the fact he's gay], anything is possible.

'Simply talking about it in public is a huge step for me. Up to this point, I have had a heterosexual lifestyle, so living with a man is really new. One step at a time.'

Penny remains a regular visitor to Bridwell Park, and now lives just 200 yards away. She has supper with Ivar and James once a week, they walk their dogs together and she has holidayed with them and the girls in Verbier.

They even spent last Christmas all together in the exquisite Georgian mansion which was fully restored after being consumed by fire in 1990.

(When Ivar moved in, in 1997, it had what he calls a builders' finish. 'The house was settling. I always told friends it was like living in a new-build Barratt house. They used to laugh and say "Ivar, how would you know?" ')

Her proximity to Ivar and James has caused some confusion locally.

James reveals: 'I went to a village yoga class with Penny and people thought I was her new boyfriend. She had to tell them, "No, he's Ivar's, not mine." '

In fact, James has become a great friend of the former chatelaine of Bridwell Park and when he's missing, Ivar knows James will be in Penny's kitchen drinking coffee and having a moan.

'I can say Ivar did this or he said that… after all, she's been there too.'

In the past year, Bridwell Park has become one of most sought-after wedding and corporate party venues in the West Country, and Lord Ivar and James now hope to break into the film and TV location market. Lord Ivar has invested about £750,000 in the business, offering accommodation for 48 guests and hosting parties for up to 160 in its new orangery.

They offer full, exclusive use of their stately home, a gambit which has proved so successful he and James must shortly move out and into a more modest four-bedroom lodge on the estate.

'Well,' says Ivar, 'I have learned you can only sleep in one bed and sit on one chair, and frankly a big house is a pain if you leave your glasses upstairs and need them downstairs in the office…'

One gets the message that wherever James is, he'd be happy.

Listening to their story has been both touching and thought-provoking. It makes you realise how the speed of travel towards acceptance of homosexuality has accelerated in recent years. For this isn't just about finding love in mid-life, it's about morality and courage and being true to yourself, no matter what your background.

As Ivar says: 'I am a lot happier now, though I am still not 100 per cent comfortable with being gay.

'In an ideal world, I know the girls would like their mother and father still to be together, but they love their 21st Century family that we have built too. Their father has a boyfriend. It's that complicated and that simple, but finding James means I will not have to lie to anyone or grow old on my own.'