Bradley Cooper has paid tribute to the UK's "magical" Glastonbury music festival, where part of his upcoming film A Star is Born was shot.
"I didn't want to make a movie about music without it being an element," the actor turned director told reporters at the Toronto Film Festival on Sunday.
Cooper, 43, surprised fans in 2017 by appearing ahead of Kris Kristofferson's set on Glastonbury's Pyramid Stage.
He plays a troubled rock star in the film, which also stars Lady Gaga.
Gaga plays a young singer who Cooper's character takes under his wing in his directorial debut.
Live performances at Glastonbury and California's Coachella festival feature in the film, a cautionary tale about substance abuse and the price of fame.
The film had its world premiere at the Venice Film Festival last month and has been hotly tipped to win Toronto's influential People's Choice award.
Previous Hollywood-set versions of the story featured Janet Gaynor and Judy Garland, while Kristofferson co-starred with Barbra Streisand in the music-based 1976 version.
"Kris happened to be playing so I asked him if I could take up some of his set," Cooper said of his appearance at Glastonbury. "We had four minutes and it was unbelievable.
"I spent four days there in all and learned so much about its inner workings.
"It's the largest privately-owned music festival in the world and it is the place that makes and rejuvenates careers.
"You watch major, huge musicians still get nervous about playing on the Pyramid Stage. It's still this place of fear and beauty."
Lady Gaga, whose real name is Stefani Germanotta, said she hoped the film would encourage people to be more proactive when seeing others in distress.
"What would be wonderful is if we intervene early when we see people struggling, both in the music industry and in life," she said.
"Fame is very unnatural, so I think it's important that we guide artists and take care of them psychologically as they begin to rise."
A Star is Born marks Gaga's first lead performance in a fictional film and features several live performances - a condition she insisted upon before agreeing to appear.
"I wanted to be a vehicle for Bradley to tell this beautiful story," she said, revealing she had shunned make-up and dyed her hair its natural colour to play rising star Ally.
"I wanted to give it everything I had.
"I feel very lucky to be here," she continued on Sunday. "And I'm here totally because Bradley believed in me."
The 32-year-old said she was open to further film roles in future but was focusing at present on her Las Vegas residency, set to begin in December.
The singer also confirmed that she had fully recovered from the health problems that forced her to bring a premature end to her world tour in February.
The Toronto Film Festival continues until 16 September. A Star is Born is out in the UK on 5 October.