The paper added that the baby was already in Portugal at the family home in the resort area of Vilamoura and Ronaldo traveled there to meet his new boy June 29 after Portugal was eliminated from the World Cup.
Speaking to Diario de Noticias, his sister Katia said the baby resembled his father. "He has brown eyes and brown hair like Cristiano."
"He's very happy, of course!" she said of her brother. "Who isn't happy having children? The baby looks like him, although he's still very small to see what his features will be like."
"He's very calm. He just eats and sleeps," she said.
It appears Ronaldo had always planned to have children. In a recent interview, he cryptically said that day might come "sooner rather than later."
Even before then, Ronaldo was talking about having a baby before marriage. In a 2007 interview with Hello! magazine, he said he often fantasizes about being a dad.
"The idea of the responsibility frightens me but also excites me," he said. "When I am with the children in the family I get broody."
Ronaldo also dresses up every year as Santa Claus and surprises the children in his family.
The soccer star said in 2007 that he hoped any future son would want to follow in his footsteps.
"I would be very proud if my child became a footballer and had similar characteristics to me," he admitted.