Diangana has joined the newly-promoted Premier League side for £18m on a five-year contract.
The 22-year-old England youth international came through the Hammers academy but spent last season on loan in the Championship with the Baggies, where he scored eight goals in 30 league games to help Slaven Bilic’s men gain promotion to the top flight.
Having become a mainstay in the West Ham midfield for 16 seasons after coming through the club’s youth ranks, Noble is disgusted one of their own has been allowed to leave so early.
"As captain of this football club I'm gutted, angry and sad that Grady has left, great kid with a great future!!!!!" Noble tweeted in response to West Ham's announcement of Diangana's departure.
In their defence, the West Ham hierarchy explained they sanctioned Diangana’s sale to help manager David Moyes strengthen other areas of the squad.
"The decision to sell Grady has been made reluctantly but - ultimately - in the best interests of the club and with the aim to strengthen the squad in different areas at this time," a statement on West Ham's official website read.
"The money received for Grady will be reinvested entirely in the team, in line with the manager's targets.
"We believe that this will give us the best possible chance of ensuring we have a balanced squad to compete in the Premier League and capable of reaching our objectives and ambitions this season."
