Answer:
First - his war tactics, prior written to support the French army, were used by German to attack and defeat France soon after.
Second - he fought for liberty and freed France to the Nazi's hands, but when he became president, his actions isolated France from Europe and the rest of the world.
Step-by-step explanation:
After World War I, de Gaulle began to write military books advocating in favor of the tanks as a perfect and suitable war weapon, and to create new military tactics, faster and precise. These ideas were not well received by his commanders because, at that moment, they didn't understand that the world was changing, and after World War I, the way to fight would never be the same. De Gaulle's book was well-received by Hitler and his generals who follow the rulers described there and created new tactics that were used against France. That was de Gaulle's first irony. The second was in the 1950s and 1960's when he was France president. He did not allow France to be part of NATO, criticized the U.S. involvement in the Vietnam war, and refused the entrance of England in the European Community (formerly the Common Market). The irony, in this case, is that he fought for freedom in the past, but his actions as a leader only reflect the opposite.