Magnusson told The Sun: “The whole situation left me very frustrated.
“We were so close to signing Darren and thought everything was in place to conclude what would have been the biggest transfer in West Ham’s history.
“I was really looking forward to making an announcement to our fans as we continue our plans to take this club forward and challenge the best teams in England.
“West Ham acted in good faith in discussions throughout with Charlton, the player and his representatives.
“The deal we put in place seemed to work for everybody concerned. Throughout the negotiations all the signs were positive. Therefore I was surprised when I learned Darren had decided not to join us.
“I feel let down and disappointed. But it is time to move on.
“In the aftermath of this I have been encouraged by the reaction of the West Ham supporters. I visited some of their internet chat sites.
“They appreciate the efforts we made and they are less disappointed than I thought they might be. The view seems to be that perhaps this wasn’t the best deal we could do at this stage.
“I’d like to think this experience will eventually stand us in good stead. There’s no doubt about it, lessons have been learned.”