Dissolution of the Soviet Union:

On September 10, 1987, after a lecture from hardliner Yegor Ligachev at the Politburo for allowing these two unsanctioned demonstrations in Moscow, Boris Yeltsin wrote a letter of resignation to Gorbachev, who had been holidaying on the Black Sea. Gorbachev was stunned – no one had ever voluntarily resigned from the Politburo. At the October 27, 1987, plenary meeting of the Central Committee, Yeltsin, frustrated that Gorbachev had not addressed any of the issues outlined in his resignation letter, criticized the slow pace of reform, servility to the general secretary, and opposition from Ligachev that had led to his (Yeltsin's) resignation. No one had ever addressed the Party leader so brazenly in front of the Central Committee since Leon Trotsky in the 1920s. In his reply, Gorbachev accused Yeltsin of "political immaturity" and "absolute irresponsibility." No one backed Yeltsin.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What was Gorbachev's reaction to Yeltsin's resignation?
stunned