The Holland defender is leaving Bologna for Napoli this week.
Former Juventus midfielder Beltrame played with Beukema at Go Ahead Eagles and told TMW: "He's a great guy, but when he's on the pitch, competitively, he's unmatched. A strong and modern defender even then. He's good with his feet and very intelligent. He has character and doesn't let anyone walk all over him.
"In fact, when he needs a dressing down, he gives it. Even then, you could tell he'd blossom. The following year, he was a regular starter, and it was a crescendo."
On Napoli, Beltrame also said: "It's the right place because it will allow him to make a further leap compared to Bologna, no offense to the Emilians. He'll get along well with (Antonio) Conte, and he'll immediately have a great connection with (Leonardo) Spinazzola.
"I know Leo well; we played in the Juventus youth team. We shared a room in boarding school."