Nadim and Tanya Ednan-Laperouse, with their son Alex, prepare to speak to the media outside West London Coroners Court, Friday Sept. 28, 2018, following the inquest into the death of Natasha Ednan-Laperouse, 15, seen on poster, who died after suffering a fatal allergic reaction on a flight from London to Nice after eating a Pret a Manger sandwich at Heathrow Airport.

A second customer of restaurant chain Pret a Manger died after eating a sandwich containing an allergen that was not noted on the label, the company has confirmed.

The coffee-and-sandwich business has promised to improve its labeling following criticism at an inquest last month into the death of 15-year-old Natasha Ednan-Laperouse, who died in 2016 after eating a Pret baguette that contained traces of sesame.

The company said an investigation was underway into a second case, in which a customer died in December after eating a supposedly dairy-free product that contained dairy protein.

Pret a Manger blamed a supplier of its dairy-free yoghurt. But the supplier, CoYo, said Sunday the allegation was "unfounded."

The parents of Ednan-Laperouse, who are campaigning for stronger allergen warnings, said they were "incredibly saddened to learn of someone else losing their life from allergens in their food."