What

"When Dina Gold began searching for the Berlin property seized from her family by the Nazis in the 1930s, she had little idea she would unearth a dark secret – how the SS paid millions in premiums to insure a key part of x-gu://item/mobile.guardianapis.com/items/world/2015/jan/27/auschwitz-short-history-liberation-concentration-camp-holocaust to what is still one of Germany’s top insurance companies." (The Guardian.)

Is "what" a fused relative pronoun in the paragraph above?