A letter has claimed that the Norwegian princess Märtha Louise was more deeply involved with a gin launched to mark her forthcoming wedding than previously stated, amid growing questions over the use of her name on the bottle. The royal, who will marry the American businessman Durek Verrett in a four-day fjord-side wedding in Geiranger, Norway, next month, is not permitted to use her princess title in commercial contexts. But the couple have come under heavy criticism, and are under investigation by health authorities, over the launch of a wedding gin that used their names and a monogram and referred to her title on the label. “We created this gin for the wedding of Princess Märtha Louise and Durek Verrett in Geiranger in August 2024,” the label on the raspberry, blueberry and blackcurrant gin stated. It comes two years after Märtha Louise renounced her official royal duties. Her father, King Harald V, decided she would keep her royal title but she pledged to make clear the difference between her business activities and role as a member of the royal family – including not using her title in connection with “commercial activity”. A spokesperson for the princess, Carina Scheele Carlsen, previously described the inclusion of her title as a “mistake” and said it would be removed from future batches. But that claim is being called into question. According to a letter from the gin producer Oslo Håndverksdestilleri (OHD) to the Norwegian directorate of health, seen by Aftenposten, the couple were involved in the label design process. The producer also wrote that it was the princess’s own idea to make a gin for the wedding and to sell it on the open market at the state-run Vinmonopolet alcohol retailer. The letter, dated 15 July, says: “Both DV [Durek Verrett] and ML [Märtha Louise] have been involved in the design of the text on the bottle.” It was also agreed, it adds, that “OHD was to make the product available for purchase at the wedding, and that OHD could launch the product at Vinmonopolet”. Carlsen and the palace declined to comment on the latest claims and OHD did not immediately respond to the Guardian’s request for comment. The Norwegian directorate of health confirmed it was looking into the case “as part of our mandate to supervise compliance with the Norwegian prohibition against advertising of alcoholic beverages”. Øyvind Giæver of Norwegian directorate of health said: “It is not our place to confirm claims made by Aftenposten, but I can confirm that the letter they quote is among the documents we have received as part of the process. Until we reach a conclusion in August/September, we cannot comment further.” The wedding celebrations are due to begin on 29 August in Ålesund where the bride and groom will travel by sea with their guests to Geiranger. The wedding, two days later, will be a private event at the 197-room Hotel Union.