Adriana, 39, and her husband Leandro, 37, have been together for seven years and have a six-year-old daughter.
"I can't believe that you're telling me this"
The couple, who refused to reveal their surnames, spent their lives trying to find their respective mothers, who were both called Maria, and had both abandoned their children when they were still babies.
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But, when Adriana contacted a radio station in the city to ask for help in finding her long-lost mum, they dropped a bombshell on the happy couple.
Adriana and her mother were reunited live on air with Radio Globo's The Time Is Now programme, which specialises in finding lost relatives.
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At the end of the segment, the mother revealed she also had a son who didn't know her called Leandro.
Suddenly realising that her husband is also her brother, an emotional Adriana said: "I can't believe that you're telling me this.
"Leandro is my husband."
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She added: "Now I'm scared to go home and find out that Leandro doesn't want me anymore. I love him so much."
Adriana and Leandro have since told Radio Globo that they will stay together as husband and wife, despite the bombshell that they are actually brother and sister.
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Adriana said: "Only death is going to separate us. All this happened because God wanted it to happen.
"Of course it would have been different if we had known all this before, but we didn't and we fell in love.
"At first we were really knocked by it all, but we had a family meeting and told everyone that we are going to stay husband and wife, whatever anyone might think."
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"We have so many plans together. Nothing is going to break us up. Nothing."