Mason Mount said Erik ten Hag's Manchester United blueprint convinced him to leave boyhood club Chelsea.
The 24-year-old midfielder is Ten Hag's first signing of the summer in a transfer deal worth an initial £55m, plus a possible £5m in add-ons.
Mount has signed a five-year contract with the option for a further year.
"Having met with the manager, and discussed his plans, I couldn't be more excited for the seasons ahead," said England international Mount.
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"Everyone can see that the club has made big steps forward under Erik ten Hag.