Serena Nikkhah, the executive fashion editor of UK Vogue, was waiting to cheer on Peregrine Hood, son of the 4th Viscount Bridgport, who was competing in the race.
Mr Hood, an Old Etonian foreign exchange dealer at Morgan Stanley, spoke of the “terrible uncertainty” he endured for about half an hour before discovering his fiancée was safe.
“She literally ran for her life,” he told the London Evening Standard. “I was getting ready to finish when I heard a bang.
“The headphones were on, the euphoria was setting in and then I got a ghastly feeling that something was wrong. Then there was massive confusion, people running, so I just stopped and started moving away.”
Miss Nikkhah, who was caught up in a crowd of panic-stricken spectators and runners, expressed her relief at having survived.