Telefonica is Telecom Italia's largest shareholder but the two have had a tense relationship for years since they also compete in Brazil.

Vivendi said on Thursday that it would enter into exclusive talks with Telefonica over the sale of GVT, picking the Spanish group over a rival bid from Telecom Italia.

Vivendi will get 4.66 billion euros ($6.14 billion) in cash from Telefonica, and a 12 percent stake in the new company in Brazil, which will be formed by Telefonica's Vivo mobile carrier and GVT.

About one third of those shares in Telefonica Brasil SA could be exchanged for a 5.7 percent stake in Telecom Italia if Vivendi so chose. That would give the French group 8.3 percent of Telecom Italia's voting rights.

(Reporting by Leila Abboud and Gwenaelle Barzic; Editing by Andrew Callus)