The German beauty has been dating Jackson since 2006, following her divorce from French actor/director Guillaume Canet.
Just two weeks ago she told reporters she never wanted to remarry, insisting, "I won't ever marry again. Does it matter if you sign a piece of paper? It doesn't make it last. I would get married to Josh at 60 if we were still together because then it really means something if you say it's for life.
But Kruger has prompted speculation she's preparing to wed once more after sporting the sparkling jewellery on Thursday night (13Aug09) as she attended a special screening of her new movie Inglourious Basterds at New York's Museum of Jewish Heritage.
A representative for the star was unable to be reached for a comment as WENN went to press.