Their relationship was so badly damaged that in the winter of 2003, having embarked on a second period in office, both threatened the other with resignation.
In the second part of his memoirs, entitled “I am not convinced – the Iraq war and the Red-Green years”, Fischer says Schröder left him dangling in the wind by announcing his absolute opposition to the American-led invasion of Iraq.
“With that, our room for manoeuvre in the security council was reduced to nothing,” writes Fischer in excerpts from the book printed in Der Spiegel over the weekend.
Referring to a speech Schröder made at an election rally where he made unequivocally clear that Germany under his leadership would not support an invasion of Iraq, Fischer said this left him nowhere to go.
“Because of the chancellor's speech we found ourselves in a situation of ‘all or nothing' and that was exactly the kind of situation I had wanted to avoid,” wrote Fischer.
“In short I was stuck, and that absolutely.”
During the days afterwards the two men, who led a Social Democrat-Green coalition government from 1998 until 2005, had a number of long face-to-face conversations, said Fischer.
He said his fear was that Germany would be completely isolated on the international political scene.
“If France and perhaps also Russia and China had been on our side, we would have had no problem. But what if we stood at the end of the day with our ‘No' alone with Syria?” he wrote.
As it happened, France joined Germany in opposing the invasion, but both saw their relations with the US and Britain damaged as a result.
The personal relationship between Fischer and Schröder suffered during the period – even though Schröder's opposition to the invasion was often credited for the coalition's re-election in late 2002.
“The fronts between us increasingly hardened,” wrote Fischer, leading to what he called growing mistrust between them.
Since leaving office Fischer has taken on consulting work for BMW, energy firm RWE and the Nabucco natural gas pipeline project. Schröder called early elections in 2005, signalling the end of the Red-Green coalition, after which he joined the board of oil company TNK-BP, a joint venture between BP and Russian partners.