I have a question about the usage of "in." Could you please explain the use of "in" in the following sentence? I don't think "what" takes a preposition, so how is "in" being used here? Why "in" is grammatically needed ? The following is an excerpt from an article in The Guardian enter link description here:
Prince Harry, who is training to become an army air corps helicopter pilot, served on the frontline in Afghanistan last year in what was widely seen as a public relations triumph for him and the British army.