Belgian debittered black malt? I'd take a guess at SPECIAL carafa III?
Special carafa III is regular carafa III with the husk removed before roasting to limit the bitter notes in roast barley.
In a pinch I'd also use black malt because it aims to do a similar thing. The husk isn't removed, but far less bitter and astringent than roast barley.
Blackprinz is also debittered black malt, similar (superior IMO) to special carafa III.
While all these malts are different at normal amounts (few percent) they are fairly interchangeable. While the beer WILL be different, I'm not sure I could pick out which was which or tell you what was different without knowing.