Proprietary estoppel in the context of disputed wills and estate claims arise where property or land has been promised to person A but the land is then gifted by will or intestacy to person B.   Person A may seek to challenge the gift by arguing that the owner should not be allowed to break his promise.
To succeed with such a claim, person A will need to establish the following;
A clear promise having been made; and
That person A relied on that promise; and
That person A will suffer a detriment if the promise is not fulfilled.