Reports have said her body was fed to dogs.
The jury's verdict on the death of victim Eliza Samudio was read out by Judge Marixa Fabiane Lopes Rodrigues at Brazil's Contagem Court of Justice in the early hours of Friday.
"The conduct of the crime of murder has sordid details and demonstration of absolute ruthlessness," the judge said in her verdict.
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"The defendant Bruno Fernandes believed that by having the body consumed, impunity would be granted."
The 28-year-old Bruno, who played for Brazilian first division sides Atletico Mineiro and Flamengo, has been in custody since July 2010. His contract with Flamengo was suspended when the murder came to light.
As well as hiding the body, he was also found guilty of kidnapping the son he had with Eliza, but his former wife Dayanne Rodrigues was absolved from the charge as it was considered she was put under pressure.
Prosecutor Henry Vasconcelos said the murder in June 2010 was carried out by another man known as 'Bola' with help from Bruno's close friend Macarrao, who was sentenced to 15 years.
Bola's trial is set for April 22.
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