T.R. Knight, who plays surgical intern Dr George O’Malley in hit TV show Grey’s Anatomy, has recorded an advert to mark National Coming Out Day in the US.

The Gay Lesbian Alliance Against Defamation (GLAAD) today premiered the 20-second spot, which features Knight telling viewers how important it is to accept their gay friends and family members.

National Coming Out Day is observed in the US every October 11th.

This year is especially meaningful, as 2007 marks the 20th anniversary of the 1987 Gay and Lesbian March on Washington and the unfurling of the AIDS Memorial Quilt on the National Mall.

In October 2006 T.R. Knight made history, becoming the first actor to publicly come out while appearing on one of America’s top-rated shows.

“More and more gay people like T.R. are living their lives openly and honestly,” said GLAAD President Neil G. Giuliano.

“T.R.’s coming out has had tremendous impact in terms of creating awareness, understanding and acceptance.”

The advert is part of GLAAD’s new “Be An Ally A Friend” campaign featuring 22 entertainers from television, film and sports.

The commercials encourage people to be allies to lesbian, gay, bisexual and transgender people and to help combat homophobia, directing viewers to GLAAD.org

T.R. Knight’s coming out caused a media scandal when it was revealed that he had been the subject of homophobic taunts from co-star Isaiah Washington.

He called Knight a faggot during an on-set confrontation last October, but at the Golden Globes in January he denied the incident had occurred.

After the ceremony, where the show won best drama, he said to journalists, “No, I did not call TR a faggot. Never happened, never happened.”

GLAAD then demanded that Washington apologise for using the word again when denying he used it in the first place.

The actor then signalled his desire to put the controversy behind him by co-operating with GLAAD.