Brazil's 2007 world footballer of the year Kaka completed his transfer from Serie A side AC Milan to Real Madrid late on Monday, both clubs announced.
The 27-year-old signed a six year contract with the Spanish giants for a reported fee of 65million euros which both clubs refused to confirm.
If it is 65million euros it would be the second biggest ever transfer - after that of French great Zinedine Zidane, who cost Real Madrid 75million euros in 2001.
Kaka had earlier undergone in Brazil a problem-free medical attended by Real Madrid's Dr Juan Carlos Hernandez as well as the Brazilian squad's doctor, Jose Luiz Ronco.
Kaka - who is in Brazil for their 2010 World Cup qualifier with Paraguay - is expected to appear at a press conference.
Real chairman Florentino Perez has established a 200 million euro war chest for players, vowing to create a "spectacular team" capable of overtaking arch-rivals Barcelona - who won the title, Champions League and Spanish Cup in coach Pep
Guardiola's first season in charge - next season.
Perez oversaw the era of the "Galacticos" when he was in charge at Real between 2000 and 2006, when world stars such as Zidane, England's David Beckham and Brazil's Ronaldo were attracted to the club.
Kaka has been at AC Milan since arriving from Sao Paolo in 2003, scoring 70 goals in Serie A and 23 in the Champions League.
He has won the 2007 Champions League with them, the 2004 league title, two European Super Cups and the world club championship in 2007.
He had been the subject of a massive transfer offer from English Premier League side Manchester City in January but the deal eventually came to nothing.