Sister Rita Callanan called the Convent of the Sisters of the Immaculate Heart of Mary her home — and she thought she would stay there until her last days, the Daily Mail reported.

Instead, the 80-year-old nun struggles with ill health and breast cancer and is now flat broke over a legal battle involving pop singer Katy Perry, who purchased the convent.

What happened?

In a convoluted legal case, Jose Gomez, who heads the Roman Catholic Archdiocese of Los Angeles, sold the property to Perry in 2015, according to published reports.

But Callanan and her late fellow nun, Sister Catherine Rose Holzman, believed they held the deed to the property and had the right to sell it. Holzman collapsed and died in the courtroom last week while the case was being heard.

The two had sold the sprawling property to a restaurateur in 2015 for $15.5 million. The buyer planned to turn it into a boutique hotel. But Perry and the Archdiocese sued the restaurateur, Dana Hollister, in 2015.

"It's caused us so much duress," Sister Callanan told the Daily Mail. “I had to go for a chest X-ray as I thought I had pneumonia. I wanted to turn my back, but I couldn't. I've been the one leading the charge, I couldn't leave this."

She added: "Does it affect my health? Yes, it does. My doctor knows what [the archbishop] is doing. She’s a Catholic, but she's not practicing because of this man. I ask God: 'What's going on?' 'Course it makes you question your faith. But I've got to believe. I have to say: 'Lord increase my faith.'"

Perry has said she plans to use the 22,000-square-foot Mediterranean-style property to “sip green tea and find herself."

Sister Callanan said she found out about the Perry sale from a realtor friend.

The archdiocese told the Daily Mail its main concern "is and has always been the care and well-being of all the IHM Sisters." Several other sisters who lived in the convent have already moved to another site.

"It's been a horrible fight for women who have been in religious life for so long who have done so much for our archdiocese. It was our property, we had the deed, he said he had the authority and had a letter from Rome from his friend that wasn't even recorded. It was a lie," Sister Callanan said.

Sister Callanan told the Daily Mail she will accept outcome of the court case, either way.

Could this impact other convents?

Still, Sister Callanan believes it is a “test case.” That means if the nuns lose the case, any archdiocese could claim ownership of convents in its area, she said.

"If he can take our money, so can any archbishop or cardinal anywhere, the other sisters are watching us," Sister Callanan said. "Instead of standing up with us and fighting, they're hiding their money, pretending they haven't got any, as they don't want this to happen to them.”