How Should I Explain Dual Employment and Termination in My Job Applications?

I was terminated from MNC (A) Company because, in my previous company, I was engaged in dual employment at (B) and (C) Company, and I did not mention (C) Company in my CV when joining MNC (A) Company. The termination was noted in my experience letter from MNC (A) Company.

Reasons for Termination and UAN History

What reasons can I provide for both terminations and the UAN history to HR/Company when joining a new company so that they will accept it? The UAN portal shows service history for both (B) and (C) companies.

Background Verification Concerns

During Background Verification (BGV) by another company, will MNC (A) Company disclose the reason for termination or not?

Consequences of Concealing Dual Employment

I am surprised to note that you concealed the fact of your dual employment in your CV while applying. I am also not surprised that you got terminated on this account by the company. You should have obtained a proper relieving letter from your previous employer. By not doing so, you have not only cheated the previous employer but also the new employer by concealing vital facts of your previous employment. Now, you have faced the consequence of termination by the current employer, and you must have sent your resignation to the erstwhile employer too. Therefore, you must take care in the future while applying.