“I want to say a big thank you to all the people involved at Everton,” the 24-year-old Belgian international striker said.
“I want to thank the fans for your support throughout the four years we’ve spent together.
“I can proudly say it was an honour to play in front of you.”
Everton’s record Premier League goalscorer with 68 posted his comments on Instagram from Los Angeles where he is on holiday with now United team-mate Paul Pogba.
United’s pre-season tour is in serendipitous fashion beginning in Los Angeles.
Lukaku added: “To the staff at the the stadium and training ground thank you for making me feel home from the first day I walked in.
“To technical staff thank you for helping me become a better player. Working with you guys has been a pleasure and I’ll take your advice throughout the rest of my career.
“Thank you Everton football club.”
Lukaku — who Everton made a tidy profit on having bought him in 2014 from Chelsea for £28m — joins United after turning down the most lucrative contract offered by the Merseyside club at the end of last season.
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