The Hammers youngster has headed back to his former club until the end of the season.
The young midfielder has spent most of this season on loan at Championship side MK Dons, but was recalled by the Hammers after falling down the pecking order.
He was unlikely to feature in West Ham’s first team though, with manager Slaven Bilic currently enjoying a plethora of options available to him in central midfield.
And after the deal was confirmed, he tweeted his excitement at getting back to work for the Addicks.
Thanks to everyone for the messages, I can't wait to put the red shirt on again and do everything I can to help the team CAFCofficial!— Diego Poyet (@diegopoyet7) January 4, 2016
“Thanks to everyone for the messages,” he wrote on Twitter.
“I can't wait to put the red shirt on again and do everything I can to help the team CAFCofficial!”
Charlton will now be hoping that the young Uruguayan can make a positive influence on the side as they seek to escape a relegation battle this season.
They are currently 23rd in the table and winless in eight games, while they also have the third worst defensive record in the division, having conceded 42 goals already.