Diagouraga joined the Bulls after a successful loan spell from Watford
Peterborough United have signed midfielder Toumani Diagouraga from Hereford United on a four-year deal for a fee believed to be about £200,000.
The 22-year-old, who Posh tried to sign from the Bulls last summer, finalised the move after being held up in Paris for the last two days.
He told the club website: "The ambition the club showed was first-class and that has persuaded me to join.
"When the opportunity came to talk to Peterborough I jumped at the chance."
Hereford director of football Graham Turner said there was a clause in the player's deal that allowed him to talk to other clubs.
"The disappointment of relegation led to him believing he could play at a higher level," Turner told BBC Hereford and Worcester.
"That has been proved by the fact that it is a Championship club that has come in for him."
Diagouraga was the subject of interest from Posh a year ago but opted to remain with the Bulls, who had just been promoted from League Two alongside Darren Ferguson's side.
While Peterborough passed straight through League One into next season's Championship, Hereford were relegated back to League Two.
And Turner added: "I would have liked Toumani to be here with us next season and [manager] John Trewick felt the same so we would not have sold. But the crux of the matter is that Toumani wanted to leave.
"He has done very well for us over a couple of years and he still had two years to run on his contract, but there was that clause in there.
"In the end we have got to do a deal and there is not a lot of money going around football at our level at this time," he added.
"If the money isn't available for future transfers at our end, it will certainly boost our turnover.
"We're allowed 60 percent of turnover for players' wages, so there will be a little bit of scope for John Trewick."
Meanwhile, Peterborough are still waiting on a response from Grimsby regarding their offer for centre-back Ryan Bennett.
Director of football Barry Fry says the 19-year-old is keen to move and if he were to do so, it would be a record transfer for the club.
He said: "We've spoken to the agent and the club and the player is very keen to move to us, subject to his own personal terms being agreed of course. But first the club's got to agree the financial package."
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