The last Pope to celebrate the old rite as Pope would’ve been Paul VI.
The last Pope to celebrate it before becoming Pope was Benedict XVI. Francis was ordained after the new rite was in force, and to my knowledge there is no record of him ever celebrating the old Mass.
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.