There no half or full citizen ship in India. Now a days peopel can keep dual nationalities. After having some other countries natinality he will not lose the his Indian nationality. This GR came before two years.
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Yes.Dual citizenship is possible.You have to apply and there is a fee that you pay.Ministry of Home Affairs will help.Since you have the Overseas Citizen card you will have no problem.MHA has a website from where you can down load the info.Get to google