The French traveller, Le Laboureur described him as a child: extremely vivid, lean and agile.

He was also seen as being quick-minded, he was a fast learner, and by the age of seven, he was fluent in not only Polish but German too, and made good progress in Latin.

The prince willingly dressed in the Polish fashion, which still further strengthened his position as candidate and endeared him to the Poles themselves.

According to some, it came from overeating certain fruits, while others claimed that he contracted dysentery from the Pomeranian voivode, Gerhard Dönhoff (1590–1648).

With the death of his only legitimate son, Ladislaus IV's grief was so great, he did not even attend the funeral, held in Krakow, where the young prince was buried at Wawel Cathedral.