The heavy cluster knockout reaction ¹⁶O(¹²C, 2¹²C)⁴He performed for the first time, reveals the true nature of the ¹²C-¹²C interaction. The observed cross section is enhanced by almost 2 orders of magnitude over the conventional zero range distorted wave impulse approximation (DWIA) predictions. An attractive ¹²C-¹²C optical potential, as obtained in the folding model, does not explain the enhanced cross section in the finite range (FR) DWIA framework. The inclusion of a hard core of fairly long range ~3:65 fm explains the data. The present investigation of ¹⁶O(¹²C, 2¹²C)⁴He along with the ¹²C-¹²C elastic scattering also proves beyond doubt that the folding model’s deep attractive heavy ion potentials are unsuitable to describe the highly overlapping heavy ions. The application of FR-DWIA opens up new avenues to use the heavy core knockout for the detailed investigation of heavy as well as Borromean halo nuclei.