HBO was lucky when illness struck the “House of the Dragon” set at the very last minute.

Director Greg Yaitanes – on the West of Westeros podcast hosted by Entertainment Weekly – discussed how they avoided delays in filming the season finale when the actor who plays one of the Cargyll twins contracted COVID-19. Arryk and Erryk are portrayed by 33-year-old actors and real-life identical twins Luke and Elliott Tittensor.

Read more: ‘Game of Thrones’ prequel keeps dragons, adds diversity

Yaitanes claimed that Luke stepped up to fill in for Elliott during filming a crucial part of “House of the Dragon” season 1 finale after the latter contracted COVID-19 on the second day of filming. The scene included Corlys Velaryon (Steve Toussaint) returning to Dragonstone, before Ser Erryk informed Rhaenyra Targaryen (Emma D'Arcy) and her council that Otto Hightower (Rhys Ifans) had arrived to negotiate terms.

On the podcast, Yaitanes remarked, “There's that scene, that big scene where Corlys comes down and they're putting the markers on the table and the messenger comes in.” He claimed that the sequence required more than two days to film and that Elliott Tittensor, one of the twins, tested positive for COVID-19 at that time.

Yaitanes explained, “So we swapped him out with his brother.”

Read more: HBO chief: Sorry, fans, no 'Game of Thrones' do-over

It’s unlikely that even the most discerning “House of the Dragon” fan would have noticed the difference unless Yaitanes had mentioned it.

Yaitanes remarked that if they hadn’t had access to a similar-looking actor, it might have been disastrous since they were ready to film D’Arcy and Erryk was nearby.

Even though the “House of the Dragon” crew avoided delay for that brief moment, they were unable to totally prevent COVID-19 during the 2021 filming. The crew member’s positive test result caused production to stop for two days in July 2021, according to Radio Times.

Read more: 'Game of Thrones' final season to debut on April 14

But now that “House of the Dragon” season 1 has aired, viewers will have to pray that the next season doesn’t see any further delays since production may only begin in 2023, according to co-creator and executive producer Ryan Condal.