HOA Board election fraud?

I am a Board Member of our HOA. We had the election for 2 positions at or annual meeting in June 2016. 3 people ran for the positions. One current Board Member (lets call him the current Secretary) and a Member at large was elected. The positions are two year positions. This year after the Annual meeting, a different member at large confessed to me he had altered the Proxy Ballot signed by the President. He thought she just forgot to check all her votes. The Secretary only won by (1) vote. Is this position legal? He would have tied with the loser. Is the election legal or do we need to have a special election to correct the action?