What big news was Edward Grey informed of about Serbia at the beginning of the movie?

He gave information that Serbia had been given an ultimatum.

Explanation:

British Foreign Minister Edward Gray said that Serbia had been given an ultimatum and that specific demands had been brought before the country because of its involvement in the Sarajevo Assassination. He also points out that it is almost impossible to fulfill the conditions that are set before the country and that they can only be seen as a way to declare war on one country. In history, this event is known as the July Ultimatum.