Portugal's Cristiano Ronaldo reacts after a missed scoring opportunity during the 2010 World Cup second round soccer match against Spain at Green Point stadium in Cape Town June 29, 2010. [Agencies]

LISBON - Portugal captain Cristiano Ronaldo announced on Sunday he has fathered a baby boy with a woman who has chosen to remain anonymous and with whom he has agreed to keep exclusive guardianship of the child.

"It is with great joy and emotion that I inform I have recently become father to a baby boy," Ronaldo, the world's most expensive player, said on his Facebook page.

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"As agreed with the baby's mother, who prefers to have her identity kept confidential, my son will be under my exclusive guardianship."

The Real Madrid forward said no further information will be provided on the subject and asked "everyone to fully respect my right to privacy, and that of the child, at least on issues as personal as these".

Ronaldo, 25, captained Portugal during their World Cup campaign in South Africa, which ended with a 1-0 defeat to neighbours Spain in the second round last Tuesday.

The winger, who moved to Real Madrid from Manchester United for a record fee of 80 million pounds ($121.2 million) last year, played in all four of Portugal's World Cup matches, scoring one goal.