Elizabeth Smyth, 61, claimed the former husband of Deirdre Romanes, 60, persuaded her into changing her wishes days before dying from cancer in May 2010.
Ms Smyth claimed that Iain Romanes, 66, persuaded his ex-spouse to sign documents which made £3,000,000 available to pump into the debt ridden Dunfermline Press media group.
She said that the change robbed her of almost half of what she would have received from an earlier will.
She also claimed the last minute change benefited Monaco-based Mr Romanes, who held a substantial stake in the newspaper publishing company.
Ms Smyth, of Kells, County Meath, Eire, took the case to the Court of Session earlier this year in a bid to have the May 2010 will set aside in favour of its 2008 equivalent.
But in a written judgement issued at the court on Thursday, judge Lord Glennie ruled that Deirdre hadn’t been influenced by Iain when she changed her will.
Saying that the businesswoman’s decision making abilities hadn’t been affected by the powerful painkillers, she was taking for her cancer, Lord Glennie wrote: “Her sister is the biggest loser by these changes. She cannot accept that Deirdre wanted to do this.
“Having heard all of the evidence, however, having listened carefully to and read the pursuer’s submissions and having given the matter careful consideration, I am satisfied that the pursuer’s case must fail.”
During proceedings at the court earlier this year, Lord Glennie heard how Mr Romanes returned to Edinburgh for the last two weeks of his former wife’s life in May 2010.
Mrs Romanes was in charge of the Dunfermline Press which owned several local newspapers and other media outlets throughout the UK.
The company later went into receivership but Mrs Romanes and her fellow executives spent time trying to save the firm.
The court heard how Mr Romanes left Deirdre nine years earlier for another woman but spent time with Mrs Romanes in the her home in Heriot Row in the heart of Edinburgh’s New Town.
The court heard that during this time, close family members were kept at arm’s length.
Mrs Smyth claimed that her sister was taking powerful painkillers during the final weeks of her life. She said this affected the judgement of Mrs Romanes, who was initially diagnosed with breast cancer in 2004.
She also claimed that Mr Romanes influenced Deirdre into changing the terms of her will, something which he denied doing.
During proceedings, Mrs Smyth questioned Mr Romanes about the events leading up to Deirdre’s death.
He said he could not recollect being at a meeting which discussed childless Mrs Romanes’ legacy in May 2010 - even though a note by one of her executors indicated he was at the meeting in the drawing room of his ex-wife’s house.
The former husband also said that the changes in Mrs Roman’ legacies - estimated at more than £4,000,000 - were the culmination of a long process.
He told the court: “This had been going on for months. I don’t know when Deirdre had begun discussions about changing the will but it certainly wasn’t something spontaneous after I arrived.”
He said that papers had already been drawn up by the time he arrived back in Edinburgh.
When asked why her late sister had changed her mind so dramatically with regards to her will, Mr Romanes said: “I don’t think this was dramatic. It wasn’t spontaneous. It was planned by Deirdre for several months beforehand.
“I don’t see why you use the word ‘dramatic’.”
Mr Romanes also told the court that he thought his ex-wife would have supported her executors who resisted Mrs Smyth’s challenge to the 2010 will.
On Thursday, Lord Glennie wrote that there was no evidence to prove that Mrs Romanes’ decision to give £3,000,000 to Dunfermline Press had been influenced by another party.
Lord Glennie also concluded that Mrs Romanes’ decision making hadn’t been affected by the powerful drugs she was taking for her illness.
He wrote: “It is clear that the decision to use some of her capital to help rescue the company did not come ‘out of the blue’ at at all.
“It was a matter which was under discussion for quite some time.
“I accept the evidence given by a number of witnesses that the company meant everything to her and she was determined to do what she could to help save it.
“Unless there was incapacity or unless undue pressure or influence was used to procure the deed or will in the form in which it was executed, then the deed or will must stand.
“There is no basis for setting it aside.”