Ivan IV (Ivan the Terrible) physically assaulted Yelena Sheremeteva the wife of his eldest son and Heir apparent Ivan Ivanovich, causing her to have a miscarriage.
Ivan in moment of rage confronted his father and soon an argument would start up, eventually leading to the topic of the failing Livonian war and the need to liberate Pskov from Polish troops. Ivan IV would claim his son was instigating an insurrection which Ivan would deny. On an impulse Ivan would try to strike at his son but instead of hitting him in the temple like OTL he hits the shoulder greatly hurting his son but not dealing a fatal blow, in defence Ivan attacked his father and pushed him to the floor grabbing his father's scepter and began beating his father with the weapon. Boris Godunov who was present would try to stop the fighting and managed to pull Ivan off his father but it was to late Ivan the Terrible lay on the floor with his face broken coughing blood and begging for help his son realizing what he had down began crying and wailing over the sin he had committed.
Boris would attempt to get aid but by the time he returned the Tsar lay dead on the floor and his son crying at his lifeless body.
1581 - 1600 Collapse of Order, Foundation of the Second Tsardom
Ivan Ivanovich was crowned Ivan V of Russia upon the death of his father on the 21st of November. The Ceremony was one of complete silence as the new Tsar accepted his throne reluctantly and half the court fearing for their lives, only Boris knew that the whole event was an accident and would remain fearless of the new Tsar. Ivan V would immediately set about trying to liberate Pskov despite the tensions in court due to his perceived need to end the war in a victory to honor his dead father. Another army would be set up to help liberate Russian lands currently under Polish occupation.
Ivan V would personally lead the troops that would attempt to relieve Pskov and after a few months of fighting thanks to the new troops would somehow break the hold of Polish troops. From there the Russian troops under Ivan would head south to meet up with the second army in attempt to expel Commonwealth troops from their soil, the attempts would bring mixed results but would ultimately push the Poles to accept a truce with Russia for the next 14 years which would allow the Poles to fight the Prussians and Swedes now fighting in their lands.
The victory at Pskov and the cease fire allowed Ivan to gain respect as a military leader and earned him the loyalty of the troops directly under him but the murder of his father had left many amongst the nobility afraid of him. Those resentful for the measures taking by his father to limit their power declared rebellion on the 20th of April 1582, declaring Ivan V an usurper, Many flocked to their banner and a base of operations was established in southern Russia near the border with the Commonwealth. The commoners at first cared little but Ivan was a butcher in their eyes only the army that fought with him was truly loyal and the troops under Boris who knew the incident to be an accident.