In response to a letter by the Protestant pastor Michel Leplay published in the French newspaper La Croix of March 22, 2018, which contained this affirmation: "As far as I know, Mary has never appeared to a Protestant," a reader wrote back:
Except in a small village called Notre Dame de l'Osier (Our Lady of the Reed), in France! In March 1657 the Virgin Mary appeared to a Huguenot called Pierre Port-Combet who had a strange experience, 8 years’ prior, when he was wounded and began bleeding while he was cutting reeds, on March 25, 1649, a Marian feast day.
As a good Protestant, Pierre showed real skepticism about this event, even in front of the "Beautiful Lady" who appeared to him. But she finally dispelled his incredulity when she mentioned his approaching death. Deeply moved, he accepted to receive the sacraments of the Catholic Church on his deathbed.
This is an approved apparition of Mary to a Protestant!
Adapted from an article by René Fantin