In 2004, supermodel Petra Nemcova was enjoying a dream vacation in Thailand with her boyfriend, fashion photographer Simon Atlee, when a tsunami devastated their bungalow.

Atlee was swept up in the chaos as he called out Nemcova’s name. Nemcova, then 25, survived by clinging to a palm tree for nearly eight hours.

ABC News’ Diane Sawyer interviewed Nemcova in the months following the tragedy. Now, 20 years after one of the deadliest natural disasters in modern history, Petra sat down with Sawyer again to reflect on the horrors of that day and the kindness of strangers who got her out alive.

“It’s always difficult to go back to the moment my life changed,” Nemcova told Sawyer in an interview that aired Thursday on “Good Morning America.”

Nemcova and Atlee were packing to leave a resort in Khao Lak on December 26, 2004, when the tsunami struck, sending huge waves crashing into their bungalow.

As the water pulled her outside, Nemcova managed to cling to the top of a palm tree, where she clung for almost eight hours before being rescued.

“I fell into this stillness, almost a meditative state, because I knew that if I panicked you lose more energy,” Nemcova said of the time. “And it took all my energy to stay alive.”

As she clung to the tree, Nemcova said she heard the screams of people calling for help, including small children.

“I couldn’t swim to them or help them because I couldn’t move my legs,” she told Sawyer in her original 2005 interview.

When Atlee’s body was found and formally identified on March 3, 2004, he was among nearly 230,000 people believed to have died in the disaster, which also affected parts of Indonesia, Sri Lanka, India, the Maldives, Myanmar, Somalia and Malaysia .

For Nemcova, it was a miracle of kindness that saved her. When she was found, her clothing had been torn off by the storm and she had suffered a broken pelvis and internal injuries.

The people who rescued Nemcova were strangers who gave her clothes and placed her on a floating mattress to steer her through the rubble to medical attention, she said.

“These people were willing to risk their lives for strangers,” Nemcova said of their rescuers. “And that shows you the best of humanity.”

Tune in to “Good Morning America” on Friday, December 20th at 7pm EST for more on Diane Sawyer’s interview with Petra Nemcova.