By ANTONIA HOYLE, in London, and SIMON PARRY, in Assam, India

Last updated at 08:18 11 February 2008

As she poses on the red carpet at tonight's Baftas ceremony, Julie Christie will present the self-assured public face of an actress at the top of her profession.

Her confidence is not hard to understand: she is heavily tipped to win the Best Actress category for her performance as an Alzheimer's sufferer in the acclaimed film Away From Her - and it is predicted she will also go on to claim an Oscar.

Yet despite her success, Julie remains as elusive as ever about her private life. Indeed, she has even refused to confirm reports that she wed her long-term partner, journalist Duncan Campbell, in November last year.

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The actress's famously aloof facade has also helped her keep another astonishing secret - a secret that has haunted her since her childhood and which can be revealed today by The Mail on Sunday.

At the centre of Julie's private drama lies a key figure she is never known to have spoken of, never met, and, according to acquaintances, has gone to every effort to block out of her mind: her secret half-sister.

The girl, called June, was the result of a relationship between Julie's father Frank St John Christie, the manager of a tea plantation in India, and one of his Indian tea-pickers.

Both daughters grew up on the stunning plains of Assam in North-East India and, on the surface, it was Julie, with her outgoing nature, pretty blonde charm and feisty sense of fun, who had the better deal.

Yet it was half-Indian, plain and studious June who was favoured by Frank - a girl from whom Julie and the rest of her British family were keen to distance themselves and anxious to forget.

Julie went on, of course, to become an Oscar-winner, achieving A-list status with films including Darling, Dr Zhivago and Don't Look Now and snaring the likes of Warren Beatty and Terence Stamp along the way.

June, six years her senior, enjoyed a more humble career as a midwife, apparently had no male admirers, lived in a modest two-bedroom semi-detached house and favoured British sitcoms over Hollywood blockbusters.

Despite their wildly differing lifestyles, however, both women ferociously guarded their privacy.

June died, aged 70, in January 2005, having told only a handful of trusted friends about her famous relative - as reluctant to acknowledge Julie as Julie, now 66, has been to acknowledge her.

"June would tell me her sister was a famous actress but that they never had any contact," says her friend Binolian Graves, 72.

"She told me Julie didn't want to know her. She didn't boast about being related to her. It was just a fact."

Given the extraordinary circumstances of the girls' upbringing, it is hardly surprising there was little love lost between them.

Born in June 1934, June was the result of an affair between Frank and an Indian peasant on the tea estate he managed in Chabua, Assam.

Although he broke off the relationship with June's mother, barely out of her teens at the time, he doted on their daughter, taking her with him to his local Colonial Club and proudly introducing her to all his colleagues.

But in 1937 Frank met and married Rosemary Ramsden, whose family came from Hove and, like Frank, had been lured from Britain to India by the low cost of living and idyllic lifestyle.

She gave birth to their two children - Julie in 1941 and then a son, Clive. Frank kept his earlier affair a secret and continued to support both June and her mother, financially and emotionally, without his legitimate family's knowledge.

In 1947, as the British agreed to Partition, Rosemary had started to suspect her husband had had a liaison with an Indian woman but was unable to prove it.

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She left and moved to Gun Hill near Horam, East Sussex, believing life would be safer there for Julie and Clive, who were packed off to boarding school.

After she left, Frank, now managing the larger Jamirah Tea Estate, even moved June into his 19th Century colonial home, complete with swimming pool and grass tennis court.

When Rosemary came back to visit her estranged husband - staying a month at a time and never bringing the children - June, whose mother had two other daughters, was hidden away until she had left.

After hearing rumours about her husband's illegitimate daughter, a suspicious Rosemary would grill servants about his relationship with his former mistress.

As Binolian Graves, who chose June to be guest of honour at her 1959 wedding to husband Tim, puts it: "June told me that Frank's new wife didn't like the fact he had fathered an Indian child. She didn't want to know at all."

Jai Singh, 80, who was Frank's servant for the 15 years he ran the Jamirah Estate, says: "The women in Sahib [ master] Christie's life did not have a happy relationship between them.

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"When his wife came here, June would be quickly sent away to stay with the family of a local schoolmaster. The Memsahib [Rosemary] would take us to one side and ask, "Do you know where his Indian wife is? Do you know where his Indian daughter is?"'

Speaking from the overgrown ruins of Mr Christie's former plantation home, Jai adds: "We were told not to say a word about June. When Mrs Christie asked me about it I replied, "I don't know, ma'am." As soon as the Memsahib had gone home, June would return to live with her father. They were very close. He doted on her.

"There was no stigma about having an Indian daughter. It was quite common among the plantation managers. People would treat her as his daughter and she received the respect that any Sahib's daughter would receive."

Describing the girls' father as a tall, striking man who was hugely popular with his Indian staff, Jai says: "We were very surprised when we first saw June's mother. Sahib Christie could have had his pick of any woman working on the plantation. But this woman was very small and not at all beautiful."

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While Frank's refusal to turn his back on June contributed to his break-up with Rosemary, it may have also rankled with Julie, who has said of her days at boarding school: "I was loved by everyone, but it wasn't much good because my parents weren't with me."

Mohanlal Sharma, a manager at the Jamirah estate for 35 years, explains why Frank's attachment to his Indian daughter would have horrified his English wife: "In those days it was normal for the English Sahibs to take their pick of the women for a one-night stand.

"If the woman became pregnant, normally the master would not support her or her child. But Sahib Christie was an honourable man and appears to have supported the woman and her daughter from the beginning.

"When his English wife was not here, there was just the master and June. As far as I know there were never any other women in his life."

As a boarder at Convent of Our Lady School in St Leonards-on-Sea, East Sussex, and then at Wycombe Court school in High Wycombe, Buckinghamshire, the teenage Julie - described as "late", "disrespectful" and "untidy" by her teachers - was already attracting admiring glances from would-be suitors.

But with her plain appearance and shy demeanour, it seems that June - sent to a Christian boarding school in Gauhati, Assam, by her father - was not so lucky with the opposite sex.

Mohanlal explains: "When June was in her early 20s, Sahib Christie hoped she would marry one of his Indian estate managers - a man he was very fond of - but it didn't work out.

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"June and the estate manager were very close for a while and we all hoped they would marry, but something happened between them.

"The manager was a handsome young man and June wasn't beautiful. Unfortunately I think in the end that is why he didn't marry her."

Instead, she threw her efforts into finishing typing courses at the Methodist Chapel in Calcutta, where she met Binolian and lived in a Salvation Army Hostel before returning to Frank on the Jamirah Estate.

In 1960, father and daughter moved to Malaga in Spain. Frank's marriage had, by this time, unravelled irretrievably and he had little contact with his family.

But in August 1963, the year Julie's first film, Billy Liar, was released, their new life together took a tragic turn.

Binolian, now 77 and living near Perth in Western Australia, says: "June had suffered from a heart condition since she was born, and Frank returned to England and stayed with friends while she had an operation.

"The day she left hospital, he died. He had a heart attack while mowing his friend's lawn. He always said the house in Spain would be June's but never mentioned it in his will, so it went to his next of kin - his estranged wife.

"There was no offer to let June keep the house or of any funds to help her. June found herself homeless and, we assumed, penniless."

In fact, Frank had left June, whom he describes in his will as his "natural daughter", £5,000 - a considerable sum in 1963.

Her friend and former handyman George Whitehorne, 81, from Goring-on-Sea, West Sussex, says: "He was a great father when she was growing up but I very much got the impression she was left high and dry.

"But she spoke so fondly of him and went back to the crematorium in Eastbourne every year to pay her respects."

Determined to fulfil her dream of becoming a midwife, June moved to England after her father's death and slept on friends' floors before training to become a nurse at Chichester College, West Sussex.

"She worked in a cafe to make ends meet and had no time for people who couldn't be bothered to work," says George.

"She even worked on Christmas Day so she could afford her studies.

"She was very sensitive if she thought anyone had any unfriendly thoughts about her because she wasn't white. She was proud to be Indian and went back to Assam several times."

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It is a sentiment echoed by Mohanlal: "After the Christies left, June used to write letters to the servants and I would read them out for them.

"They were quite short but would say, 'I am very fond of you. I will always remember you and I have loving memories of when we used to be together."'

Whether Julie, who has never been seen at the Jamirah Estate since leaving Assam, is quite so proud of her Indian roots remains to be seen.

As one childhood friend of June's, who also grew up in Assam, puts it: "I'm Anglo-Indian. Some people are proud of it but others aren't. Who's to say what is the case with Julie?

"June didn't have any contact with her but I don't think June was unhappy about that."

Instead, June threw herself into midwifery, a profession she practised at Southlands Hospital in Shoreham-by-Sea and one which undoubtedly helped quench her maternal cravings.

Bob Chambers, a 57-year-old school security manager who lived on the other side of June's semi-detached house in Goring-by-Sea, says: "I remember once we had a party where one of our guests recognised June.

"She had saved her baby's life when his tongue got stuck in his throat. She absolutely loved her job."

She didn't watch her sister's films but was, says George Whitehorne, a fan of historical documentaries and the sitcoms Dad's Army and Keeping Up Appearances.

But her real passion was gardening, a hobby she shared with Julie, who has properties in East London and Spain but spends most of her time at her farmhouse in Montgomery, mid Wales.

According to Bob: "June chose her house in Goring because of its big garden. She loved azaleas and clematis.

"She was lovely to live next door to, always inviting us round for a prawn curry and a bottle of wine, and buying us little gifts such as chocolates and flowers.

"We bought her a glass plaque with 'Perfect neighbour' written on it, because that's what she was."

Neither Bob nor his wife Sandy, also 57, who lived next to June for five years, had any idea she was Julie's secret sister.

"I'm amazed,' admits Sandy. "She wore trendy jeans and tops but she didn't look like her at all. She went to keep-fit classes and had a wardrobe full of beautiful dresses but she never wore them."

At 4ft 10in, she was only just tall enough to see over the couple's garden fence.

"She was tiny and frail," says Sandy. "Towards the end of her life she got even thinner. We worried about her but she said she was fine."

June died on January 11, 2005. Her official causes of death are bronchopneumonia and, more poignantly, frailty of old age.

"She started going downhill six months before she died," says George, who was also unaware of her celebrity connection. "Her digestive organs weren't working properly."

It seems June - whose two sisters, mother and, of course, father, had all died of heart failure at an early age and who sent her own doctor a hamper every Christmas for keeping her healthy - simply felt lucky to have lived for so long.

"Three days before she passed away she went into a nursing home," says George.

"I told her they would build her up in there. She said, 'I don't want building up. My body's had enough.'"

The Chambers helped arrange her funeral in Goring-on-Sea. "We had to go through her address book and look at her Christmas cards to find out who to ask," says Sandy.

"There weren't many people there - and Julie definitely wasn't one of them."

Last week Julie's brother Clive, now retired from his job as a lecturer at Hull University, refused to discuss his half-sister.

The Mail on Sunday made several attempts to contact Julie Christie for comment but she failed to respond.

Whether or not the actress regrets not meeting her sibling is a secret she may well take to her own grave.

But as she walks down the red carpet tonight, she might spare a thought for the sister she never knew, yet who had such an impact on her life.