According to HBO, nearly 10 million people watched the Game of Thrones spinoff House of the Dragon on Sunday, making it the most watched series premiere in HBO and HBO Max history.
The series was also the top trending topic on Twitter on Sunday, with over 2 million Google searches that day.
Nielsen's cable-only ratings will not be available until Tuesday.
"It was wonderful to see millions of 'Game of Thrones' fans return to Westeros with us last night," said Casey Bloys, HBO and HBO Max's chief content officer. "'House of the Dragon' has an incredibly talented cast and crew who poured their hearts and souls into the production, and we're overjoyed with the positive response from viewers."
House of the Dragon is a Game of Thrones prequel that takes place nearly 200 years before the events of the latter show. It is based on George R.R. Martin's novel Fire & Blood and tells the story of the House of Targaryen.
Game of Thrones had its highest weekly audience on HBO Max last week, ahead of the premiere of House of the Dragon.