Beckham left United ten years ago.
"It wasn't my choice. At the time, it was difficult to take. The fact that I had to leave Manchester United and find another club was obviously upsetting at the time," he told BBC Sport.
"But the fact that I was able to go to a club that was as big as Manchester United, like Real Madrid, was very lucky. I am very proud of that. Not many players have been lucky enough over the years to leave Manchester United, be successful and go on to play for a club like Real Madrid. It was difficult, but there is always a silver lining."
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