Sentence:  [...] the queen was brought to bed of a son, who was baptised by the name of James. This would, if any thing could at that time, have served to establish him on the throne; but so great was the animosity against him, that a story was propagated that the child was <WSD>supposititious</WSD>, and brought to the queen's apartment in a warming-pan. 
Meaning of the word marked with <WSD> tags:  Spurious; substituted for the genuine, counterfeit; fake.