I believe that the brooch now worn by Princess Michael in various ways is the one in the photo Nellie posted.
But I think that brooch/clasp is different from the one in the set of pearls worn by Princess Marina.
Princes Marina's pearl clasp is on the left. Princess Michael's is on the right.
To my eye the shape and size of the pearls, as well as the setting, are different. I have no idea if the one in Princess Marina's necklace is the one mentioned in the magazine report.