The correct answer to your question may depend on the detailed facts of your case, which are not clear from your question.
However, here is a general answer to the issue raised in your question. It may be advisable for you to consult some lawyer by showing him full facts of your case.
Once you have obtained a divorce in Australia in 2018 (as you have mentioned), and if this divorce decree was granted by a competent court, then, depending on detailed facts, it may not be necessary to obtain a fresh divorce in India. More so, if you have acquired citizenship in Australia, as you have mentioned.
Please note that under Section 13 of the Civil Procedure Code, a foreign judgment shall be conclusive with regard to any matter directly adjudicated upon between the same parties, except in certain situations mentioned therein. Also, Section 14 of the said Code lays down that such foreign judgment shall be presumed to have been pronounced by a court of competent jurisdiction, unless evidence to the contrary is produced.
Further, a perusal of the Hindu Marriage Act (under which you may perhaps be seeking a fresh divorce) shows that its provisions may not be applicable if you are NOT domiciled now in India, as it perhaps appears to be the case since you appear to have settled in Australia by acquiring its citizenship.
However, as I mentioned above, these are general observations in the absence of knowing full facts of your case. You may please consult some local lawyer by showing him detailed facts / documents of your case.
Dr. Ashok Dhamija is a New Delhi based Supreme Court Advocate and author of law books. Read more about him by clicking here. List of his Forum Replies. List of his other articles. List of his Quora Answers. List of his YouTube Videos.