Hired as a secretary by Eleanor Roosevelt, Mercer ended up having an affair with Roosevelt's husband. Eleanor discovered love letters between Franklin D. Roosevelt and Mercer in 1918, when the presidency was just a distant ambition for her husband. Fearing for his political life, Franklin convinced Eleanor to stay married, promising he would avoid seeing Mercer again and that the two would sleep in separate beds.
Post-affair: Franklin didn't keep his promise. With help from the Roosevelts' daughter Anna, he continued to rendezvous with Mercer, and she was in Warm Springs, Ga., the day Franklin died. (Eleanor was conspicuously absent.) Mercer died in South Carolina in 1948.