MUMBAI (Reuters) - Tata Sons, parent and biggest shareholder of Tata Consultancy Services (TCS) <TCS.NS>, can only nominate a new chairman for the company but not appoint him without the approval of the board of directors, a source close to Cyrus Mistry said on Thursday.

TCS, India's No. 1 software services provider by revenue, in a statement to the stock exchange, said Mistry has been replaced as chairman by Ishaat Hussain, who will hold the post until a new candidate is found.

(Reporting by Aditi Shah; Editing by Swati Bhat)