I hadn't realized before that Eugene Delacroix (1798-1863), the leading French painter of the Romantic Era, was perhaps the illegitimate son of Talleyrand, the most glamorous name in the history of diplomacy. Wikipedia says:
There is reason to believe that his father, Charles-François Delacroix, was infertile at the time of Eugène's conception and that his real father was Talleyrand, who was a friend of the family and successor of Charles Delacroix as Minister of Foreign Affairs, and whom the adult Eugène resembled in appearance and character. Throughout his career as a painter, he was protected by Talleyrand, who served successively the Restoration and king Louis-Philippe, and ultimately as ambassador of France in Great Britain, and later by Talleyrand's grandson, Charles Auguste Louis Joseph, duc de Morny, half-brother of Napoleon III and speaker of the French House of Commons.
Are there other likely examples of one famous person being the secret child of another?