A lawyer who argued in favour of supporting California’s Proposition 8 same-sex marriage ban is now planning his lesbian step-daughter’s wedding.

Attorney Charles Cooper now says his position on same-sex marriage has evolved. He previously argued that same-sex marriage would undermine straight marriage.

He found out that his step-daughter Ashley is gay during the Proposition 8 debate. Prop 8 was struck down by the US Supreme Court last year.

Cooper’s evolution on same-sex marriage is being hailed as indicative of changing attitudes across the US on same-sex marriage.

Interviewed for Jo Becker’s book ‘Forcing the Spring: Inside the Fight for Marriage Equality’, Cooper said: “My views evolve on issues of this kind the same way as other people’s do, and how I view this down the road may not be the way I view it now, or how I viewed it ten years ago,” reports the Associated Press.