Phones4u founder John Caudwell has bought a minority stake in Ralph & Russo.

The British billionaire - who sold his Phones4u shares for £1.46 billion in 2006 - is said to have invested a huge sum in the brand, which according to his spokesman represents a ''nine figure'' valuation of the company.

The label - which was founded by designer Tamara Ralph, and company CEO Michael Russo in 2007 - counts Angelina Jolie, Beyoncé and Sheikha Mozah of Qatar among their clients and is reportedly planning to extend its offering into perfume and accessories following Mr. Caudwell's investment.

Russo told Vogue.com: ''We really weren't looking for investment at all. We'd been approached before and it wasn't something we were courting, but this deal felt really right for us.

''John has great business experience and his investment will allow us to execute our expansion and growth strategy more quickly than we had planned. It's a hugely exciting time.''

Mr. Caudwell added: ''Tamara Ralph and Michael Russo have built an extremely successful luxury brand with a great reputation and endless potential. I have no doubt that my investment will continue to elevate Ralph & Russo and I'm very excited about this inspiring and rapidly growing business.''

Despite his significant contribution, Mr. Caudwell has agreed to a ''passive investment'', leaving Ralph and Russo in full control of all aspects of the company.