Cristiano Ronaldo was presented to a near-capacity crowd at the Bernabeu after completing the formalities of his £80m world record move to Real Madrid.
The former Manchester United winger, 24, passed a medical on Monday before greeting almost 80,000 Real fans.
In his first public address to his new supporters, he said his transfer had "made my childhood dream a reality".
However, he was forced to make a hasty retreat at the end of the ceremony when some fans tried to invade the stage.
"I never imagined that fans would have such a feeling for me," said Ronaldo before his premature exit. "It was impressive. A special moment for me today."
Ronaldo retreats as fans invade
Barcelona carried off the Spanish title, Champions League and Copa del Rey last season but Ronaldo played down any suggestion that Real could immediately replicate their bitter rivals' achievement.
"If we win only the Champions League I'm happy. We need to take it step by step and later we can think about winning the treble," he stated.
Since signing for Manchester United from Sporting Lisbon as an 18-year-old in 2003, the Madeira-born forward has developed into one of the best players in the world and is the current holder of the Ballon d'Or award as European Footballer of the Year.
He claimed he is still on good terms with his former club, despite his determination to leave Old Trafford.
"I have to say thank you to all supporters, my boss, my friends and my team-mates because I'd been there six years and I had a good relationship with all people there," he insisted.
"But the people understand my decision and the people respect that. Of course it's a great challenge now and the people know my dream is to play in Madrid.
"I'm going to miss many many things in Manchester but this is the life, this is my new house, my new club and I'm going to give 100% for this club."
However, earlier in the day, he revealed his move was partly motivated by a belief that La Liga is "superior" to English football.
"I think La Liga is going to have more quality because of the players that are arriving," he said. "All the players have a lot of quality and the referees protect the players."
In the press conference that followed his introduction to Real's fans, he predicted he would notice a difference between playing styles in the two countries.
"I expect a different league. I have played six years in the Premier League, it is very different. It is faster and players are strong but here the small teams and the medium teams try and play football," he stated.
Ronaldo arrived at Madrid airport just after midday local time and travelled to the Hospital Sanitas La Moraleja for his medical as he put the finishing touches on his world record move.
"Ronaldo is in perfect condition and very eager to start the season as soon as possible," Carlos Diez, Real Madrid's medical chief, told www.realmadrid.com.
"He has an extraordinary cardiac and lung capacity. Now we will be able to start work, using an individual plan in order to improve his performance.
"For him, it's a dream and this dream starts to convert into reality from today."
The player agreed a six-year contract with Real after United reluctantly decided that they could no longer hope to hold on to him.
Ronaldo's arrival follows that of fellow big-money signing Kaka.
More than 50,000 fans turned out to welcome the Brazilian playmaker, who signed from AC Milan for a reported fee of £56m.
With Real president Florentino Perez's signings the Spanish league is superior to the English
But in a statement posted on its website, Real said Ronaldo's unveiling "could very well make history", as hundreds started to queue up outside the Bernabeu.
The previous record turnout for a player presentation occurred when Diego Maradona drew 75,000 people to Napoli in July 1984 after joining them from Barcelona.
Ronaldo was presented with the number nine shirt by the most famous player to wear it for the club - the legendary Alfredo di Stefano.
And Ronaldo had said earlier he believes Real's £200m spending spree this summer, which has resulted in Karim Benzema and Raul Albiol also moving to the Bernabeu, edges the Spanish league ahead of England's top flight in terms of quality.
"Both leagues are going to be very good but I think that with Real president Florentino Perez's signings the Spanish league is superior to the English," added Ronaldo.
"It's going to be a magnificent competition in Spain this year."
Real are reported to be lining up further big-money moves, with Bayern Munich winger Franck Ribery and Liverpool midfielder Xabi Alonso said to be on their wanted list.
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