Impulse ebay purchase, is it a fake?

[Lactodorum]

Relative newbie who started purchasing coins of emperors but bought this on ebay without doing any research.
Believe it to be an AE3 Half Centenionalis of Helena.
Inscriptions read FL HELENA AVGVSTA / SECVRITAS REIPVBLICE, so far so good.
The problem is that it has CONS in the exerge, and with a B on the left hand side. I cannot find any reference to this coin being minted in Constantinople. Apologies if I have simply missed it but would appreciate any helpful comments or guidance on where to look (as well as this site). The coin does seem to be in very good condition, perhaps too good!
Helena_ae

[Vladimir]

Hello!
This coin is recorded in RIC as # 11 for Constantinople. Two officina letters are known A and B. A is rated r4; B is r2.
Here is the description I have, but wasn't able to upload in the catalog yet (Sorry!)
Helena AE3 Constantinople "Securitas" RARE r2
Saint Helena, mother of Constantine the Great, AD 324-328 AE3
Obv: FL HELENA AVGVSTA - Diademed, mantled with necklace
Rev: SECVRITAS REIPVBLICE - Securitas standing left, lowering branch and raising a rope with right hand.
Exe: B | CONS
Constantinople mint AD 326-327 = RIC VII, p. 571, 11 Rare (B = r2)

[Lactodorum]

Many thanks for the Information (and apologies for the delay as I've been away), I still have much to learn.