love child
From Longman Dictionary of Contemporary Englishlove childˈlove child noun [countable] SCCFAMILYa child whose parents are not married – used especially in newspapersExamples from the Corpuslove child• Unlike the synonym, MAMzer, BENKert connotes love child, not one merely born out of wedlock.• She would have made the secret love child of Leon Trotsky and Margaret Thatcher look like an uncommitted, apolitical layabout.