Updated

A Cheney family feud erupted on Facebook after Liz Cheney reiterated her opposition to same-sex marriage in an interview with "Fox News Sunday" -- despite her sister Mary Cheney, who is gay, having recently married her longtime partner.

Liz Cheney, the daughter of former Vice President Dick Cheney, was asked about her position on gay marriage and her sister's personal life on "Fox News Sunday."

"Listen, I love Mary very much. I love her family very much.  This is just an issue in which we disagree," she said.

This prompted a tough response on Facebook from Mary Cheney's spouse, Heather Poe.

"Liz has been a guest in our home, has spent time and shared holidays with our children, and when Mary and I got married in 2012 - she didn't hesitate to tell us how happy she was for us," she wrote. "To have her now say she doesn't support our right to marry is offensive to say the least."

Mary Cheney also chimed in, writing: "Liz - this isn't just an issue on which we disagree - you're just wrong - and on the wrong side of history."

Liz Cheney is running for Senate in Wyoming and trailing far behind incumbent Republican Sen. Mike Enzi.

Cheney clarified her position on gay marriage in the interview Sunday, saying she doesn't support amending the Constitution to oppose same-sex marriage. But personally, she said: "I do believe in the traditional definition of marriage."