Rupert Sanders' brother-in-law claims affair with Kristen Stewart 'went on for months'

PUBLISHED: 04:59 EST, 29 July 2012 | UPDATED: 05:00 EST, 29 July 2012

Kristen Stewart called her fling with Rupert Sanders a 'momentary indiscretion' but now relatives of the British director have claimed that the pair were seeing each other for months.

Sanders' brother-in-law, Leopold Ross, has said he believes Kristen and Rupert became involved with each other while they were filming Snow White and the Huntsman.

Model Liberty Ross' brother told of how his sister made 'sacrifices' for Rupert and that she was unhappy in their marriage for a while.

More than a 'momentary indiscretion': Liberty Ross' younger brother has claimed that Kristen Stewart's affair with his brother-in-law Rupert Sanders went on for months

Speaking to The People, Leopold told that Kristen's affair with the 41-year-old director began during the second half of filming for the blockbuster movie, he explained: 'It was from the last half of filming and all through post-production, clear into last week.'

Following the news that her husband had been unfaithful, the 33-year-old, who has two young children with Sanders deleted her Twitter account, presumably due to being bombarded with messages on the micro-blogging site.

Close: Liberty Ross' younger brother has told The People that he believes Stewart started seeing Sanders as they filmed Snow White and the Huntsman

'She thought it was worth it': Leopold told of how his sister moved from Britain to Hollywood for Rupert to pursue his career

Leopold, who is a musician also spoke about the fact his sisters willingness to move to Hollywood to give Sanders' career a chance had been thrown back in her face.

He said: 'She made some sacrifices for something she thought was worth it, now she knows, right? Five minutes from her home. Doubt it was worth it but it's life.'

But positive that good will come out of the scandal, he continued: 'It might actually make things better in the long run. She wasn't that happy for a while, but our family is close, she'll be all right.'

Shortly after it was news of her relationship with Sanders become public knowledge, Kristen Stewart issued a grovelling public apology to co-star and boyfriend Robert Pattinson.

'I love him, I love him, I'm so sorry': Kristen issued a public apology to her boyfriend of three years Robert Pattinson after the news that she had an affair with Sanders, 41, broke

According to People, Kristen said: 'I'm deeply sorry for the hurt and embarrassment I've caused to those close to me and everyone this has affected.'

'This momentary indiscretion has jeopardised the most important thing in my life, the person I love and respect the most, Rob. I love him, I love him, I'm so sorry.'

Whereas, Rupert said: 'I am utterly distraught about the pain I have caused my family.'

'My beautiful wife and heavenly children are all I have in this world.'

He told People: 'I love them with all my heart. I am praying that we can get through this together.'

As details of Kristen's relationship with Rupert continues to unravel, it has now been reported that the 22-year-old actress cheated on Pattinson because she was envious of the friendship he formed with Australian beauty Emilie de Ravin on the set of Remember Me.

Sources close to Stewart said that she became 'upset' as Robert's friendship with Emilie developed, as the actors would go to bars and restaurants.