The Austrian ambassador Busbecq would note "Suleiman has among his children a son called Mustafa, marvelously well educated and prudent and of an age to rule, since he is 24 or 25 years old; may God never allow a Barbary of such strength to come near us", going on to talk of Mustafa's "remarkable natural gifts".
Duta besar Austria Busbecq mencatat "Di antara anak-anak Suleiman ada yang bernama Mustafa, yang sangat terdidik dan bijaksana serta dalam usia yang matang, 24 atau 25 tahun; semoga Tuhan tidak membiarkan barbar sepertinya datang mendekati kita", dan juga menyebut "bakat alami yang luar biasa" yang dimiliki Mustafa.