* Executive Chairman Del Vecchio takes on all powers
* Del Vecchio's close aide Milleri named CEO
* Milleri would replace Del Vecchio at merged group if he died (Adds comment from Luxottica's spokesman)
MILAN, Dec 16 (Reuters) - Italy's Luxottica has parted ways with its fourth chief executive in three years as Chairman Leonardo Del Vecchio prepares the eyewear group he founded for a planned merger with France's Essilor.
Luxottica, the biggest maker of spectacles, agreed in January to merge with the top lens manufacturer to create a 46 billion euro ($54 billion) group with a global shop network and brands from Ray Ban to Giorgio Armani and Burberry.
Luxottica said on Friday Massimo Vian, CEO for products and operations, would step down three months before the expiry of the current board's mandate as it simplified its structure ahead of the merger.
Vian's responsibilities will be handed to both Del Vecchio and his close aide Deputy Chairman Francesco Milleri, who will also take on the position of CEO. A spokesman said Chief Operating Officer Giorgio Striano would ensure continuity in the running of the industrial side of the business.
"The post-merger integration of Essilor and Luxottica is fast approaching," EXANE BNP Paribas said in a note.
EU regulators are set to clear the merger without asking for concessions, sources familiar with the matter said on Thursday. The deal still needs antitrust approval in the United States, China and Brazil.
Del Vecchio, 82, told the Corriere della Sera newspaper on Saturday that Milleri would replace him at the merged group if anything happened to him. Milleri, 58, started working with Luxottica as an IT consultant and earned the trust of Del Vecchio, becoming over time his right-hand man.
Del Vecchio and Essilor CEO Hubert SagniEeres are set to share powers at EssilorLuxottica for the first three years as, respectively, executive chairman and executive vice-chairman.
SagniEeres, 62, told the Financial Times last week the group would look to hire a chief executive at some point.
"SagniEeres has ruled himself out - as too old - which is a not too subtle indication that Del Vecchio is not in the game either," EXANE said. "Investors shouldn't expect a smooth post-merger integration path."
Del Vecchio returned to the helm of Luxottica in 2014, taking on executive powers as chairman. A legendary figure who rose from an orphanage to being one of Italy's richest men, Del Vecchio is also known for his top-down management style, taking key decisions without broad consultation.
He has presided over an overhaul of the business he founded in 1961, boosting digital investments while also expanding the retail network, centralising distribution in China and fighting online discounts of top brand Ray Ban in the United States.
He owns 62.5 percent of Luxottica and will be the single biggest shareholder in the merged group.
"In the past three years ... I've fixed and improved Luxottica to keep up with the times. And I was able to do it thanks to Francesco Milleri ... he shared every important decision," Del Vecchio told Corriere.
Vian had been appointed at the top within a dual-CEO structure put in place in October 2014, after Luxottica lost two bosses in six weeks due to frictions with Del Vecchio. Vian had remained as the only CEO after co-head Adil Mehboob Khan left in January 2016.
An engineer who had joined in 2005, Vian will pocket a gross 6.3 million euros in addition to severance pay, Luxottica said. ($1 = 0.8508 euros) (Editing by Alexander Smith and Mark Potter)