George HW Bush has attended the same-sex wedding of two friends as an official witness.
The former US president and his wife, Barbara Bush, attended the ceremony at the weekend of Bonnie Clement and Helen Thorgalsen in Maine.
Mr Bush's spokesman said he and Mrs Bush, who have ties to the area and own a compound in the coastal town of Kennebunkport, attended as private citizens.
The news became public after Ms Thorgalsen posted a photo on her Facebook account showing Mr Bush at the ceremony signing a piece of paper.
She wrote in the caption: "Getting our marriage license witnessed!"
Same-sex marriage became legal in Maine last December.
Mr Bush, a Republican and the 41st US president, was in the White House when gay marriage was not as big a political issue as it is today.
His son, the former president George W Bush, opposed same-sex marriage.