PARIS, June 28 (Reuters) - Orange, France's biggest telecoms operator, is opening exclusive talks with bank BNP Paribas with the aim of bringing its online retail banking clientele under BNP Paribas' umbrella, three sources close to the matter said on Wednesday.

The talks, if successful, would put an end to Orange's venture into the retail banking sector, which started after the acquisition of a majority stake in Groupama Banque in 2016 and represented a key strategic move by former Orange CEO Stephane Richard.

Richard's successor, Christel Heydemann, decided to get rid of the loss-making unit following a strategic review, the sources said.

But the telecoms operator, advised by M&A firm Lazard, has faced difficulties in trying to find a buyer for its online bank, which piled up more than 1 billion euros of losses since its launch, the sources said.

The end of Orange Bank's experiment would confirm the domination of French traditional lenders in the online banking field, with Societe Generale's Boursorama being the clear leader with close to 5 million clients in the country.

Other independent digital-only banks like Germany's N26 and Britain's Revolut also compete against French banks.

The BNP Paribas-Orange talks would aim to create a partnership under which Orange Bank's retail clients would be invited to become customers of BNP Paribas' online bank Hello Bank!.

Orange is set to make an announcement later on Wednesday, the sources said. A spokesperson for Orange declined to comment. (Reporting by Mathieu Rosemain; Editing by Sudip Kar-Gupta and Mark Porter)