Evidence for a second main-sequence turn-off in a deep colour-magnitude diagram of NGC 1868 is presented .
The data were obtained with HST/WFPC2 and reach down to m _ { 555 } \simeq 25 .
Besides the usual \tau \simeq 0.8 ~ { } Gyr turn-off found in previous analyses , another possible turn-off is seen at m _ { 555 } \simeq 21 ( M _ { V } \simeq 2.5 ) , which is consistent with an age of \tau \simeq 3 ~ { } Gyrs .
This CMD feature stands out clearly especially when contaminating field LMC stars are statistically removed .
The background subtracted CMD also visibly displays a red subgiant branch extending about 1.5 mag below the younger turn-off and the clump of red giants .
The significance of the secondary turn-off in NGC 1868 was confirmed with Monte-Carlo simulations and bootstrapping techniques .
Star-counts in selected regions in the cluster CMD indicate a mass ratio of old population/young population in the range 5 \% \buildrel < \over { \sim } M _ { old } / M _ { young } \buildrel < \over { \sim } 12 \% , depending on the mass function slope .
The existence of such a subpopulation in NGC 1868 is significant even in the presence of uncertainties in background subtraction .
The possibility that the secondary turn-off is associated with the field star population was examined by searching for similar features in CMDs of field stars .
Statistically significant excesses of stars redwards of the main-sequence were found in all such fields in the range 20 \buildrel < \over { \sim } m _ { 555 } \buildrel < \over { \sim } 22 .
These however are much broader features that do not resemble the main-sequence termination of a single population .
We also discuss other alternative explanations for the feature at m _ { 555 } \simeq 21 , such as unresolved binarism , peculiar stars or CMD discontinuities associated with the Böhm-Vitense gap .