Long learned his fate on Monday, exactly a week after Langdon took up the reins. However, Langdon has moved to quash speculation that a staff cull will follow.
In an internal e-mail leaked to Campaign, Langdon said: "Long's departure brings to an end the period of management instability at the agency." He added that the joint managing directors, Adam Leigh and Simon Toaldo, will be given more responsibility.
"The existing management team of the company - Nick (Hastings), Malcolm (White), Simon (Toaldo), Adam (Leigh), Christian (Hinchliffe) and Jo (Boyd) - will continue in their current roles, although I intend to give Simon and Adam increased responsibility, which I will announce shortly."
Langdon has also confirmed that he is not going to appoint another chief executive to replace Long. Long has been at the agency for ten years.
He took his most recent role following the merger of the Havas siblings Partners BDDH and Euro RSCG Wnek Gosper last year.
He joined as the managing partner at Butterfield Day Devito Hockney in 1994 and became the chief executive in 1995 and the chairman and chief executive in 2002.
Before that, he was the client services director at WCRS, where he led the team responsible for the creation and launch of Orange.
Long was unavailable for comment as Campaign went to press.