Everyone knows the story about Ivan IV Grozniy (that's Ivan the Terrible) killing his own son, and by extension, the Rurikid dynasty.
Now, part of the argument resulted from the czar/tsar's treatment of his son's wife - apparently he upbraided her for her wearing of immodest attire, striking her and causing her to miscarry.
Ivan the Younger had words with his dad about this, resultingin the fatal argument. Now, the czar/tsar argued that his son was plotting against him, which they probably would've still argued about.
Now, what if Mrs Ivan Ivanovich instead of miscarrying, goes into early labor (or even carries the child to term) and gives Ivan Ivanovich a healthy (albeit (probably) posthumous) son? When Ivan tried to get the boyars to swear to accept the succession of his infant son during Ivan's illness of 1552/1553 they did so unwillingly (prefering Vladimir of Staritsa), how does a second regency for ANOTHER three year old czar/tsar look?