Andros Townsend celebrates after scoring the first goal for Newcastle
The winger completed a move to the Eagles on Friday morning, bringing an end to his short stay at St James’ Park.
He arrived at the club from Tottenham Hotspur in the January transfer window and quickly established himself as a star man in the side.
Newcastle United's Andros Townsend looks dejected
He played a key role under Rafa Benitez as they made a late and unsuccessful bid to avoid relegation from the Premier League.
That deal included a release clause though, something Palace have used to their advantage to tempt Townsend back to London.
And Charnley has explained that Newcastle were powerless to resist the move because of that agreement in the original contract.
"Naturally we are very disappointed to lose Andros but we are bound by the terms of his contract," he told the club’s official website.
"Given our situation in January it was a condition of him joining that we included a buy-out clause."
"However, I am sure now with Rafa as our manager we will not be in a position whereby we will need to agree to clauses of this nature in the future.”
Newcastle manager Rafael Benitez celebrates with Andros Townsend at the end of the match
It now remains to be seen whether Newcastle can move to quickly replace Townsend after his departure.
They are reportedly close to completing a deal for Bournemouth winger Matt Ritchie, who could be viewed as a direct replacement for Townsend next season.
The club’s fans will be keen to see more signings arriving though as they eye an instant return to the Premier League next season.
Bournemouth's Matt Ritchie in action