"I guess no one will ever know."
Taika's humour was met with a hilarious comment from HowToDad's Jordan Watson: "It was Rita, or a piece of toilet paper stuck to the back of your suit. (See what I did there)," he posted.
Waititi's other famous friends agreed the couple nailed the red carpet.
Pop artist Benee commented with flame emojis, and actress Katie Cazorla agreed.
"WOWZA!!," she wrote, adding flame emojis to express that she thought the couple looked smoking hot.
Eternals is Marvel's latest release and is directed by Oscar-winning director Chloé Zhao, who also co-wrote the screenplay. The movie's star-studded cast includes Gemma Chan, Richard Madden, Kumail Nanjiani, Angelina Jolie, and Kit Harrington.
Waititi and Ora have gone public with their romance since August - they attended The Suicide Squad premiere in Los Angeles.
Since then, the couple turned heads at the Met Gala and were spotted looking loved up at the exclusive fashion event.
The singer and Waititi, who split from his wife Chelsea Winstanley in 2018, first sparked rumours they were dating in April this year when Ora posted a series of photos of the pair on Instagram captioned: "Good times, memories, random things on my phone and the ones I love".
The couple were then spotted together at the RuPaul's Drag Race premiere in Sydney, where the director had been filming his next Marvel film, Thor: Love and Thunder.