A former archbishop and Vatican envoy to the Dominican Republic died on Friday before he could be tried for child sex offences, an official statement said.
Jozef Wesolowski, 66, would have been the first high-ranking church official to be tried on paedophile charges. He was accused of possession of child pornography and sexually abusing children during his time as papal nuncio -- permanent diplomatic representative of the Vatican -- to the Dominican Republic, CNN reported.
"Vatican authorities quickly carried out the first investigation and have established that the death was caused by natural causes," the Vatican statement said.
An autopsy has been ordered.
His trial was delayed in July when he fell ill and was rushed to a hospital in Rome.
The Vatican said it was investigating Wesolowski two years ago, and it defrocked him last year.
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In 2014, Italy's Corriere della Sera daily reported that Wesolowski's laptop contained more than 100,000 files with pornographic images and videos, some showing naked teens ages 13-17 forced to have sexual relations with each other or with adults.
If convicted, he could have faced between six and 10 years in jail.
Before starting work in the Dominican Republic in 2008, Wesolowski was nuncio to Bolivia, Kazakhstan, Tajikistan, Kyrgyzstan and Uzbekistan.
He began his career as a priest in Poland in 1972, and became a bishop in 2000.