Whitford, who starred in Oscar nominees "Get Out" and "The Post," told Ryan Seacrest he was engaged while walking the red carpet at the Academy Awards.
"I walked out of the room and I said to my fiancee, this is unlike any script I've ever read. This could be incredibly brilliant or it could really not work," Whitford said during E!'s Live From the Red Carpet about "Get Out."
Landecker was also spotted wearing a diamond ring Friday as the couple attended the 11th Annual Celebration of the 2018 Female Oscar Nominees together.
Whitford, 58, and Landecker, 48, starred together on Amazon's "Transparent" as Magnus Hirschfeld and Sarah Pfefferman respectively.
The couple began dating in the summer of 2015.
"I knew Bradley for a year before we dated and I kind of thought that he seemed like a cocky actor boy and I wasn't really that interested," Landecker said previously to People magazine.
"Now I've learned that If I don't like someone at first, that's probably a sign that they're perfect for me because my taste is so bad ... so I was like, 'Oh, see here it is!' I didn't think and now I'm the happiest I've ever been."
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