England and Wales have taken the unprecedented step of allowing heterosexual couples to opt-out of traditional marriages and choose a civil partnership.

The change, mandated by Britain's Supreme Court last year, took effect Tuesday. The groundbreaking case had been brought by Rebecca Steinfeld and Charles Keidan who said the long legal battle had taken its toll on the couple's mental health.

Steinfeld, 38, called Tuesday’s decision "a unique, special and personal moment for us" that had been "rooted in our desire to formalize our relationship in a more modern way, focus on equality and mutual respect."

The Supreme Court’s ruling means that heterosexual couples who opt for a civil partnership (which has been available to same-sex couples since 2005) can enjoy the benefits of married couples, including marriage allowance tax relief, inheritance tax exemption and joint parental responsibility for children.

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Advocates of the change argued successfully in court that to deny heterosexual couples the same options available to same-sex couples amounted to discrimination. Steinfeld and Keidan lost their bid in a lower court but triumphed at the Supreme Court.

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"Against all odds, we succeeded in a legal battle against the government and then, they did what we asked for all along," said Keidan, 43.

The Associated Press contributed to this report.