It really depends on what you mean by "supposed to be practically in charge". Supposed by whom ? If the war rages on and the leader does not even know, then one can confidently say that the leader does not hold the actual power, which is instead in the hands of people who perfectly know that the leader is not actually leading.
One situation which is similar to what you are looking for is what happened at the siege of Szigetvár in 1566. On September 6th, the attacking party's leader (none other than Suleiman the Magnificent) died in his tent. We don't really know the actual cause (he was more than 70 at that time, so it may very well have been a "natural cause"). The inner circle of councillors kept that death secret, and the siege kept on; the day after, the Ottomans actually broke through the defences and stormed the city. For a few weeks, the war continued, and the nominal leader was unaware of it because he was already dead at that time.
If you want a situation where the nominal sovereign is kept in his closed palace, pampered by some prime minister or general, and kept aloof of the external world to the point of not knowing what happens at all, then plausible candidates are the late Merovingian kings in what would later on become France. As Wikipedia describes for the last one, Childeric III:
Childeric took no part in public business, which was directed, as previously, by the mayors of the palace. Once a year, he would be brought in an ox cart led by a peasant and preside at court, giving answers preprepared by the mayors to visiting ambassadors.
The power was really held by the mayor of the palace, an hereditary charge held by the lineage from which issued the Carolingian kings, in particular Charlemagne. We don't have day-to-day accounts of the life of Childeric III, but it is quite possible that he was not kept informed of anything except through the yearly ceremonial, in which his role was little more than that of a trained parrot.