The Tigers have already voiced their thoughts on losing one of English rugby's brightest prospects, who is leaving to Gloucester with the guarantee of a starting place.
The Kingsholm club released a statement to say the 23-year-old, whose move south has been one of the worst-kept secrets in the game for the last week, has penned a two-year deal effective from June.
The centre or fly-half, who is currently with the England Saxons squad ahead of their meeting with Ireland on Saturday afternoon, has spoken of his desire to play at number 12 - something he is expecting to be able to do with Gloucester.
Pre-empting the move, Leicester director of rugby Richard Cockerill called Twelvetrees decision to switch clubs "disappointing" earlier in the week, but the player himself insists he remains indebted to the Tigers.
He said: "I'm incredibly grateful to everyone at the Tigers for the role they've played in helping me to get to this point in my career and, of course, all the support from the fans I've had over the last three years.
"It's not been an easy decision to make but I am looking forward to joining Gloucester in the summer and being part of what is shaping up to be an incredibly talented young English back line.
"In the meantime, though, I'll be fully committed to helping make the rest of the season as successful as possible for Leicester."
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