Madrid: It's been four years since his birth, but Cristiano Ronaldo's son has no idea who his mother is.

Cristiano Ronaldo with his son Cristianinho. Pic/Getty Images
Cristiano Ronaldo with his son Cristianinho. Pic/Getty Images 

According to a report in the website yesterday, the Real Madrid and Portugal star's sister Elma said Ronaldo Jr, called Cristianinho, has stopped asking about the woman, believed to be a surrogate mother.

She added: "Once we told him she was in Heaven, but my brother and mum asked us not to repeat it. We say now his mum went travelling. He
doesn't ask anymore."

Questions about Cristianinho's mother surfaced again last week when Ronaldo's mum Dolores Aveiro released an official biography in which she revealed she went to the US to pick up Cristianinho after his birth in 2010.

She said Ronaldo, 29, told her: "The mum will never be known."

Aveiro's biographer Paulo Sousa Costa hinted Ronaldo may wed girlfriend Irina Shayk. He said: "Dolores knows sooner or later he'll get married."