As the stick-thin twin checks into a rehab centre, her sister breathes a sigh of relief.

Playing dress ups has long been a favourite past-time for twins Ashley & Mary-Kate Olsen. But as the girls tried on the lace & satin gowns they'd been sent for their Hollywood movie premiere, Ashley had a terrible realisation. "When Ashey saw Mary-Kate's stick-person body while she was changing, she knew sometimes was really wrong," says a close pal of the pair. "Nothing fit her sister properly - it was the first time she'd noticed how Mary-Kate's bones jutted out & how pale she was. Ashley didn't want to say anything to upset her, but she knew she had to help her."

It was early May, just days before their red-carpet party for New York Minute & a little more than a month before their 18th birthday. Ashley & MK, as she's known to her friends, were counting the days to June 13, when they'd finally be of age & have access to their huge $430 million fortune. "Ashley waited until the New York Minute premiere was over because she didn't want to spoil the night. But when headlines started speculating MK was anorexic, Ashley panicked & turned to their mum Jarnette. Together they called in the girls' dad David," explain the friend, who says the Olsens divorces in 1996 but have stayed close for their kids' sake.

All three soon realised Mary-Kate's life was out of control & the June birthday deadline suddenly took on a whole new significance, the source says. "She'd been wasting away before their eyes, but constantly denying she had a problem. They had to act but knew once she had her 18th birthday there was nothing anyone could do to force MK to get the help she needed. Her parents had to get her to a clinic before they lose legal guardianship over her."

Recent reports have said Mary-Kate went into a clinic of her own accord shortly after the twins' high-school graduation on June 7. But the friend says the reality was quite different. "She was dragged there by her parents before she turned 18. They were terrified that once they had no control over MK she'd self-destruct. It was a drastic move & it killed them to do it, but they had no choice. Ashley was right behind their parents. She knows better than anyone how bad things have gotten with MK."

It was another two weeks before the Olsen camp officially announced that Mary-Kate was getting treated for a 'health related issue' at an undisclosed facility, which these exclusive photos reveal is Cirque Lodge in Sundance, Utah. Eventually, Olsen publicist Michael Pagnotta confirmed to America's Us Magazine that MK was undergoing treatment for an 'eating-related disorder'. "Its a mult-treatment facility which is perfectly capable of accommodating her needs," Michael told the Magazine. "Mary-Kate has a team working with her, including a reknowned psychologist & a nutritionist, among others." According to its website, Cirque Lodge specialises in drug & alcohol dependency. Its intensive programs are designed for a minimum stay of 30 days, starting at $42 700 for the first month.

Mary-Kate pleaded to Ashley for help against their parents, unaware that she was on their side. "She couldn't believe her parents would do this. She begged her sister to back her up, but Ashley was leading the charge to get MK help before something bad happened." According to their pal, Mary-Late's food problems have been worrying for a long time. "MK stopped eating normally last year, she got it into her head that she was fat. She was always 'on a diet' & watching her weight. Even after she lost a few pounds she insisted she still needed to lose more. MK's breakfast was usually just a handful of cereal, & she'd rarely finish it. She'd refuse to eat lunch. Out with her boyfriend David Katzenberg or friends, she'd order something & pretend to eat it. Jarnie even hired someone to monitor MK's mealtimes during school because they knew she was skipping meals. But it wasn't until she really went overboard that everyone realised this was more than just a crash diet. MK started ordering salad & would only eat a lettuce lead or one tomato off the top. Or she'd order soup, take a few sthingyfuls & stir it around for the rest of the meal."

It was Ashley who lured her sister to an intervention - held under the guise of a dinner to celebrate their recent graduation - supervised by Mary-Kate's therapist. Sister Elizabeth, & brother Trent came to support their parents. Its understood David's second wife Mackenzie chose to keep their two young kinds - Taylor & Jake - out of the proceedings.

"As soon as they sat down to eat, Mary-Kate was up to her old tricks & not eating at all," the friend reveals. "As the meal went on, she started to realise this wasn't an ordinary family dinner. Her mother told her that after dinner she was going with them to a rehab centre. Then she told MK she'd be staying there & that she had no choice about it. MK tried to wheedle her way out of it, but her mother wouldn't budge. She said they couldn't force her to go, but her dad reminded her that they had a few days before she turned 18, & she had no choice but to go where they sent her. It was drastic but it had to be done. Mary-Kate was going to die if she didn't get help."