The embarrassing encounter was probably mortifying for Robbie's poor hubby, but even Margot admits, it does make for a pretty killer story.
Ellen declared Hemsworth the victor, but only because he was able to answer a question about US current events.
Robbie, 27, took the honours, quickly coming up with 1981's Physical.
Questions ranged from identifying fellow Aussie actress Nicole Kidman's birthplace to naming an Olivia-Newton John song.
"It's supposed to be me".
'I suppose so. a very hungover version of the two of us, ' he replied.
Chris, 34, also chose Liam. "Which one of my neighbors may run for president in 2020?" (Clearly, they were showing a little too much).
"The whole thing was so absurd", Robbie said.More news: Nick Kyrgios wins ATP title in Australia for first time
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After meeting Ellen and Portia, Ellen says to Margot and Tom: "Have you met Obama?"
"Tom puts on these shorts, his oldest gym shorts, and they're tiny", she said.
That's exactly the situation Golden Globe nominee Margot Robbie and her husband Tom found themselves in, the details of which were revealed in all their embarrassing glory on daytime TV. "He gets on his bicycle to ride there and I'm like, 'Woah!' You cannot wear those shorts, you can see everything", Robbie said. Unfortunately for Tom, he hadn't really packed any appropriate athletic-wear, so he ended up sporting a pair of bright pink short shorts. I was already starstuck and then she's (Ellen) like, 'Have you met Obama?' We were like, 'What?' And standing next to them is former President Barack Obama.
After DeGeneres introduced herself and de Rossi, the embarrassment continued for Robbie's husband Tom.
All three were on treadmills at the gym.
"I'm scared because my husband's going to kill me for telling this story, but it's my favourite story ever and it's the story of how Ellen and I met", Robbie began, describing how she and husband Tom Ackerley were on their honeymoon previous year in Tahiti. "In a gym that is tiny!".
At the end of the interview the talk show host gifted Robbie with a pair of long shorts to pass on to Ackerley.