An undated letter to a certain Febo (di Poggio) confirms this supposition.

It may probably be referred to the month of December.

In it he says that he means to leave Florence next day for Pisa and Rome, and that he shall never return.

Febo's answer, addressed to Rome, is dated January 14, 1534, which, according to Florentine reckoning, means 1535.
We may take it, then, as sufficiently well ascertained that Michelangelo departed from Florence before the end of 1534, and that he never returned during the remainder of his life.

There is left, however, another point of importance referring to this period, which cannot be satisfactorily cleared up.