Clue: Lanky Jane's not finished with former French diplomat (10)
Answer: TALLEYRAND
Explanation: Definition: former French diplomat
**TALL** ("lanky") + (Jane) **EYR**(e) [*'s not finished*] + **AND** ("with") 
*Charles-Maurice de Talleyrand-Périgord (1754-1838) was a French diplomat whose career spanned the regime of Louis XVI, the French Revolution, Napoleon and then Louis XVIII and Louis-Philippe.