Charlton have signed Lewis Page from West Ham for an undisclosed fee.
The 20-year-old left-back has agreed a two-and-a-half-year contract at The Valley.
He made three first-team appearances for West Ham, all in the Europa League, and has previously been on loan at Coventry City and Cambridge United.
“He’s quick, likes to get forward and is a good crosser. I really like that in a full-back,” Charlton boss Karl Robinson told his club’s website.
“I got a chance to see him during his loan spell at Coventry and he’s a left-back that fits in well with our system.
“We’re building a squad here to get into that top six and Lewis will be an important part of what we are trying to do.”
Page added: “I’m delighted to be here. I know how big the club is and I know we are pushing for promotion and trying to get up there – I’d like to be a part of that.”
Meanwhile, West Ham’s teenage goalkeeper Sam Howes has joined National League South side Hampton & Richmond Borough on loan.
The 19-year-old, who has previously been on loan at Wealdstone, is expected to stay with the Beavers until the end of the season.
Howes is set to make his debut against Bath City on Saturday.