Well, we'll never really know for certain.
A man hearing a theory knows the answer. A man hearing many theories is never sure.
There’s no basis for any of the so-called theories of alternate authors of Shakespeare — not only is there absolutely no records of any kind linking any of the so-called candidates with Shakespeare’s works, the first folio has the words of Shakespeare’s rival and friend, Ben Jonson, eulogizing William Shakespeare as the author of the works. However, this phenomenon amuses as it bemuses.