Former socialite Laura Adshead, whose breakup with David Cameron sent her straight into the nunnery as Sister John Mary at the Abbey of Regina Laudis, is now playing a supporting role in the biographical documentary called God is the Bigger Elvis.

The film title is referring to the convent’s Prioress Mother Dolores and her former life, which was also glamorous.

One-time a Hollywood starlet, Dolores Hart appeared with Elvis Presley in two of his films, Lovin’ You and King Creole, before entering the order in 1963.

With her long serge habit, make-up-free face and closely cropped hair hidden by a traditional wimple, Sister John Mary appears indistinguishable from her fellow Benedictine nuns.

Sister John Mary is devoted to a never-ending ritual of worship and work at her convent with the 36 sisters who follow the Rule of St Benedict on an isolated 400-acre farm.

It’s a life she was called to but it is hardly one the 44-year-old glamorous blonde seemed destined for when she worked in London at Conservative Party HQ – with her ambitious young boyfriend David Cameron.

Laura Adshead is a former pupil of prestigious private school Cheltenham Ladies’ College, from where she went up to Oxford – meeting David Cameron when they were young undergraduates.

Laura Adshead dated David Cameron from the spring of 1990 until summer 1991, and while he worked at Conservative Central Office, she went on to become the then Prime Minister John Major’s correspondence secretary.

Then their lives took different turns. David Cameron was selected for political stardom, while Laura Adshead left politics to study at the Wharton business school in Philadelphia.

She became an executive in Manhattan for Ogilvy & Mather, the advertising agency that inspired the television drama Mad Men – but the stresses of success, and, perhaps, of personal rejection, finally proved too much for her.

Laura Adshead descended into a world of drinking and addiction before finally finding salvation in God at the abbey in the Connecticut hills, three hours north of New York City.

“I did think my life would progress on the normal tracks of meeting someone, marrying, having children, but that’s not the path that God has led me,” Sister John Mary says in a new documentary revealing her story.

Laura Adshead, who was once David Cameron’s girlfriend, is now Sister John Mary

Photographs are shown of her when she was a young woman, posing in a leopard-skin top, dragging on a cigarette and savoring a glass of wine.

But she admits that her lifestyle then brought her little except loneliness.

Sister John Mary says: “I feel like I tried most things in life that are supposed to make you happy. That journey took me down into alcoholism and drug addiction.”

It has been suggested that her downward spiral may have started soon after her break-up from the future Prime Minister David Cameron.

In a 2007 biography of David Cameron, a former colleague of the pair at Conservative headquarters recalled Laura Adshead being granted a “period of compassionate leave” to recover from the heartbreak.

The authors say David Cameron was also shaken by the split and its aftermath, and add: “Perhaps as a result of the fall-out from his affair with Adshead, Cameron thereafter dated women outside politics.”

Laura Adshead later went out with the historian Andrew Roberts, one of David Cameron’s friends.

Laura Adshead dated David Cameron from the spring of 1990 until summer 1991

When she moved to New York to work as a strategic planning director at Ogilvy & Mather, Laura Adshead found herself part of a social whirl that included aristocratic Europeans and American trust fund heirs.

Newspaper diaries chronicled her presence at society events – at one polo match she mingled with Prince Albert of Monaco, Estee Lauder’s granddaughter, Aerin, and a billionaire polo-playing friend of Prince Charles, Peter Brant, who is married to model Stephanie Seymour.

Laura Adshead spent freely, renting a $24,000-a-month summer home with pool and tennis court in the exclusive enclave of The Hamptons on Long Island, regarded as the summer seaside playground of America’s wealthy elite.

But by 2008 Laura Adshead had apparently become overwhelmed by problems with substance abuse, and declared that she had decided to become a nun. She recalls: “I remember having to tell my mother, <<I’m going to join the abbey>>, and she said, <<Yes, I can see this world has no real meaning for you any more>>. I looked at this place and saw women who had what I wanted.

“You make a decision here to surrender your life to God.”

Laura Adshead seems to have embraced the lifestyle wholeheartedly. The film shows the formal ceremony that she went through in order to join the order of nuns.

She is seen dressed in a smart fuchsia dress and knotted pearls – then happily allowing the sisters to untwist her long blonde hair from a bun and cut it back.

A wimple is then placed around her head before she is introduced to the congregation by her new name.

“This is the only place I could see myself being – because this is where it’s at,” she says.

Sister John Mary is seen at prayer, weeping with emotion.

“She really is committed to the abbey,” said a source who met her at a service to which the public were admitted.

“Her mother and sister were at the service. The nuns chanted in Latin. It was very beautiful.”

Laura Adshead took her vows four years ago, but formation lasts for as long as five-and-a-half years.

Only at the end of this apprenticeship will she be eligible to take holy orders and assume the title of “Mother”.

To outsiders, the regime at the Abbey of Regina Laudis may seem harsh. The first bell of the day rings at 2:00 a.m. to announce Matins.

Then it clangs at first light, again at 8:00 a.m. for Mass and then at regular intervals until Vespers, at 5:00 p.m.

Chores for interns such as Laura Adshead include mopping the chapel floors, tending a herd of dairy cattle and scrubbing the pails that senior nuns use to churn butter.

Laura Adshead is embracing the lifestyle, despite the apparent hardships.

“A monastic life, this is where the struggle is,” she says in the film.

“There’s no way out. You don’t get to leave and go to a movie.

“You don’t get distraction from all the human emotions. It’s like this hothouse where things get worked out.”

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