The former Girls Aloud singer and X Factor judge is starring as Jenny in 2:22: A Ghost Story.
The Girls Aloud stars attended the press night of new stage show Fantastically Great Women Who Changed The World.
The former One Direction singer called his ex the “best mum in the world”, adding: “I couldn’t ask for someone better."
“Although we knew this day would arrive I am somehow still feeling at a loss for words."
Many Twitter users have suggested that a Black artist or broadcaster would have been a more appropriate host.
The singer celebrated turning 38 with her bestie and former bandmate, Kimberley Walsh.
The former X Factor judge and Girls Aloud singer won't go back to being as busy as she was prior to her break.
The former Girls Aloud singer has broken her year-long social media silence.
The band have sparked speculation they could reunite for their 20th anniversary in 2022.
It's also been announced Twiggy will be joining Mama Ru and Michelle Visage on the BBC Three series.