The winger is United’s first signing of the summer, arriving at Old Trafford in a £15m deal from Swansea.
While James will join the ranks of famous Red Devils, his girlfriend Ria Hughes will become the latest Old Trafford wag.
Hughes, 21, who works as a sports instructor, has been dating the footballer for two years.
And she made an emotional statement, paying tribute to her man’s achievement on her social media account.
In a post shared earlier today on Instagram, she wrote: “Even after all these years you still manage to amaze me every single day.
“You work so hard on and off the pitch at everything you do.
“Your determination, your personality, how you deal with things, how selfless you are, how you treat people, your dedication, the ambition you have, just everything about you makes me so bloody proud.
“What a dream of yours this is – I still can not believe it is happening.
“I’m so lucky I get to watch you achieve your goals everyday. Forever grateful.
“There is no better person who deserves this more. Keep working hard. Keep being you. I am so proud.”
James spoke of his delight at becoming Ole Gunnar Solskjaer’s first summer signing.
But he admitted the occasion ‘was tinged with sadness’ after his father died suddenly last month at the age of 60.
He said: “This is one of the best days of my life and a challenge I am really looking forward to,” said James who only made his professional debut for Swansea in February last year.
“The Premier League is the best league in the world and Manchester United is the perfect place for me to continue to develop as a player.
“This is an incredibly proud moment for me and my family, however, it is tinged with sadness that my father isn’t able to share this experience with us.
“I am looking forward to working with Ole, meeting the team and getting started.”