Singer Sir Elton John – who two years ago famously denounced gay marriage – will perform this month for the American Foundation for Equal Rights (AFER), a group formed specifically to support a challenge to California's gay marriage ban, Proposition 8.

Sir Elton, who along with his partner, David Furnish, welcomed a baby boy on Christmas Day, will perform a concert on January 19 at the Beverly Hills estate of Ron Burkle.

A three-judge panel heard oral arguments in the appeal of Proposition 8 last month, but a ruling is not expected for months.

Sir Elton bitterly chided gay marriage backers after voters approved the ban in 2008.

“What is wrong with Proposition 8 is that they went for marriage,” Sir Elton told USA Today. “Marriage is going to put a lot of people off, the word 'marriage' … I don't want to be married. I'm very happy with a civil partnership. If gay people want to get married, or get together, they should have a civil partnership … Heterosexual people get married. We can have civil partnerships.”

Sir Elton and Furnish entered a UK civil partnership in 2005.