I just finished watching the latest CNG auction and this exceptionally rare coin just hammered for 3k...I was not even close; but congrats to the new owner.
CNG description--
Constantine I. AD 307/310-337. Æ Follis (23mm, 4.14 g, 6h). Londinium (London) mint. Struck circa AD 311. Laureate and cuirassed bust right / Radiate, draped, and cuirassed bust of Sol right. RIC VI –; C&T 6.04.001. Brown surfaces, a bit rough, flan flaw on obverse. VF. Extremely rare.
From the Paul DiMarzio Collection. Ex Roma E-Sale 17 (25 April 2015), lot 1017 (hammer £550).
About this issue, C&T write: “There are only six known examples of this coin type, all struck from the same reverse die, and the two obverse dies illustrated.”