Ansel Elgort has denied claims he sexually assaulted a 17-year-old girl in New York in 2014.
The US actor was accused by a Twitter user identifying herself as Gabby, on Friday, in a now-deleted post labelled "my story with Ansel Elgort".
The Baby Driver star responded online saying: "I cannot claim to understand Gabby's feelings but her description of events is simply not what happened."
He says they had "a brief, legal and entirely consensual relationship."
The actor, who was 20 years old at the time, went on to apologise for the way it ended, admitting that he just "stopped responding to her" and "disappeared".
'Work to grow in empathy'
"As I look back at my attitude, I am disgusted and deeply ashamed of the way I acted. I am truly sorry," said Elgort, who is now 26.
"I know I must continue to reflect, learn, and work to grow in empathy."
In Gabby's earlier account of events, she said she was "sexually assaulted a couple days after I turned 17," after messaging the star on Snapchat, when she was "just a kid and was a fan of him".
"Finally I'm ready to talk about it and finally heal," she wrote.
"I just want to heal and I [want] to tell other girls who have been through the same as me, you're not alone."
She said she had suffered from panic attacks and PTSD since the alleged incident.
In his lengthy response, Elgort said he "was distressed" to see what was being written about him on social media.
The actor has previously appeared in films including The Goldfinch, Paper Towns and The Fault In Our Stars. He is due to star in Steven Spielberg's West Side Story later this year.
You can access information and support about sexual assault here.