U2 frontman and anti-poverty campaigner Bono is reported to have made an estimated €420m profit after seeing the value of his shares in the social-networking site Facebook soar in recent weeks.

The singer is a partner in the private equity firm Elevation Partners, which is believed to have purchased around €155m in Facebook stock from private shareholders last year.

The move brought the company's overall stake in the privately owned company to 1.5% at the time.

However, this stake has now quadrupled in value after the company received fresh investment from Goldman Sachs and Russian investment firm Digital Sky Technologies earlier this month.

This led to a $50bn (€37bn) recent valuation of Facebook, leaving Bono and his firm sitting on a paper profit of some €420m.

There has been speculation for some time that the company intends to float on the stockmarket, a move which would allow Elevation to cash in its shares if it wishes to do so.

Bono and his fellow band members in U2 have previously been the target of protests after they decided to move part of their tax affairs to the Netherlands to avoid paying tax on their royalties in Ireland.

U2 moved their publishing arm to the country in 2006 after the government capped tax-free earnings for artists at €250,000.

Previously, U2 had been one of the biggest beneficiaries of Ireland's granting of tax-free status to artists for royalty earnings.

In a 2009 interview with The Irish Times, Bono said he was "stung" and "hurt" by criticism of the band for moving part of its business to the Netherlands to lessen its tax burden.

"We pay millions and millions of dollars in tax. The thing that stung us [about the criticism] was the accusation of hypocrisy for my work as an activist," he said.