Story highlights Man claims to be brother of Christian woman sentenced to death for apostasy in Sudan

Al-Samani al-Hadi says the woman he claims is his sister should recant or be executed

Woman's husband says he had never seen al-Hadi before his wife's trial began

Western leaders have decried the verdict and asked Khartoum to free the woman

Two names and two families at the heart of a tragedy.

Al-Samani al-Hadi is one of three brothers, and what he calls their "private family business" has captured the attention of the world.

"Firstly I want to say, I am the brother of the convicted woman Abrar al-Hadi", he tells CNN in his first sit-down interview since the woman he claims is his sister -- known as Mariam Yahya Ibrahim in media reports -- was sentenced to death by a court in Sudan for abandoning the Muslim faith.

The woman, 27, was raised as a Christian by her mother and is married to a Christian man. But because her father -- who deserted the family when the woman was a child -- was Muslim, the courts consider her to be the same and asked her to recant her faith. She refused, and is now languishing in Omdurman Women's Prison, just outside Khartoum.

"Her name isn't Mariam, her name is Abrar al-Hadi. I am al-Samani al-Hadi Mohamed Abdullah, her full -- older -- brother," al-Hadi, speaking to CNN from an Islamic Center in Omdurman, tells us as he rattles off dates and details in an attempt to prove this is the sister he grew up with.

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He says she started primary school in 1992, and middle school eight years later. He even remembers the score she got on a critical exam -- "she got a 73.7 percent," according to al-Hadi.

Al-Hadi says his mother and brothers attended their sister's university graduation ceremony in Khartoum. Nothing, he says, seemed amiss.

Then, he says, she met her husband Daniel and his sister. He claims Daniel -- whom he called "the Priest" -- fed his sister "potions" to convert her to Christianity.

Daniel Wani and his wife tell a very different story. They say they were introduced through his sister in 2009 and married in 2011. Mariam, as Wani calls his wife, was a committed Christian -- attending church with a frequency that far outstripped his own.

Wani says he never saw the man claiming to be his brother-in-law until the trial began.

When I put this to Al-Samani al-Hadi, he tells me: "Then she is lying to both the Christians and the Muslims."

"She went missing in Ramadan [July] last year for 45 days. That's when we went to the police. When she was picked up we found her face was different, the way she looked at us was different. She was bewitched.

"When she stood in front of the court she said her name was Mariam Yahya. We were shocked."

The case dragged on for seven months, during which time they brought fingerprint and identity documentation, photocopies of which have since been disseminated to local reporters. The documents -- which the court ruled to be genuine -- purport to show that the fingerprints recorded for the national identity card issued in the name of "Abrar" at the Sudanese government registry offices were an exact match to those the court took from Mariam.

Wani told CNN that even if his wife is released, he fears for his family's safety from al-Hadi and his brothers.

Wani is a U.S. citizen and is attempting to secure asylum there for his wife, along with citizenship for his two children.

That process, he says, is being delayed by U.S. demands for paternity testing of the children. When asked by reporters earlier in the week if this was true, State Department spokeswoman Jen Psaki said, "Genetic testing is a useful tool for verifying a biological relationship."

Mariam -- or Abrar -- is currently hoping her that the courts will believe the story of her life as she tells it, according to her husband. She insists that she was brought up by a Christian mother and has never practiced Islam. And in spite of visits by religious scholars and Sudanese government officials pressuring her to recant, it's a story she's sticking to.

I found myself returning to the same question time and again in this interview -- is al-Hadi really prepared to see the woman he claims is his sister killed?

"It's one of two; if she repents and returns to our Islamic faith and to the embrace of our family then we are her family and she is ours. We are prepared to hold her dearer than the apples of our eyes. But if she refuses she should be executed."

Even as all eyes are on Sudan's Court of Appeal, for al-Hadi there is no turning back.

"Why would I indulge my humanity, my emotions and incur the wrath of my Lord? That's not how it works for us."