The Aquaman actress, 36, took the stand in a court in Fairfax, Virginia to testify in the defamation trial between herself and her Pirates of the Caribbean actor ex-husband.
Amber has claimed Johnny, 58, “slapped” her when she asked him about a tattoo on his arm.
Speaking in court, Amber said: “I will never forget it – it changed my life.”
Get exclusive celebrity stories and fabulous photoshoots straight to your inbox with OK!’s daily newsletter.
Amber then claimed the first time Johnny hit her was over a conversation about a tattoo on his arm.
She said: “I was sitting on the couch, we were having a normal conversion, there was no fighting, no nothing. He was drinking and I didn’t realise at the time, but I think he was using cocaine, he had a jar of cocaine.
“I asked him about the tattoo he has on his arm, it looked like black marks, I didn’t know what it said… and I asked him what it said – he said ‘Wino’…
“I laughed because I thought he was joking, and he slapped me across the face…”
Johnny had a tattoo on his arm that read “Wino Forever”, previously for his ex girlfriend Winona Ryder.
Amber then added: “And I laughed because I thought ‘this must be a joke’ – I didn’t know what was going on.
“I just stared at him, kind of laughing, still thinking he was going to start laughing and was going to tell me it was a joke.
“He said: ‘You think it’s funny bi**h, you think you’re a funny bi**h?’
“It was clear it wasn’t a joke anymore. I stopped laughing but I didn’t know what else to do.”
Amber then claimed how when the Edward Scissorhands actor hit her the first time, the second slap soon allegedly followed and she later lost her balance and ended up on the carpet.
She went on: “He slapped me again. It wasn’t a joke anymore. I stopped laughing. I didn’t know what else to do. He slapped me for no reason.”
Amber continued: “Second slap I know he’s not kidding.
“It wasn’t a joke anymore. I stopped laughing. I didn’t know what else to do. He slapped me for no reason.”
She went on: “I lose my balance. I’m all of a sudden realising the worst thing has happened to me that could possibly happen to you. I wish so much he was joking. It didn’t physically hurt me.”
Amber then described what she claimed to be the moments immediately after the slap.
“I was sitting there on the carpet, looking at this dirty carpet…” She said. “I just sat there thinking how much time do I have because, God did he just me? No, I didn’t want to leave him, to have the man I was in love with leave. I knew it was wrong and I had to leave him and it broke my heart because I didn’t want to leave him.
“I wish I could sit here and say I walked out of that house and drew a line and stood up for myself but looking at the dirty carpet trying to will myself to get up and walk out the door. I stood up and looked at him in the eye and looking at him and before I know it he starts crying. I’d never seen an adult man cry.”
Johnny then began apologising, according to Amber, as she claimed: “He’s touching my knees, saying, ‘I’m sorry baby, I thought I put the f**ker away, I thought I put the monster away’. He’s on his knees.
“I just remember thinking he was crying, he seemed so sorry but I couldn’t forgive him because it means it will happen again. I got up in my car and walked to my car and didn’t say anything.
Become an OK! VIP and you will unlock access to all of our big exclusives…
Be the first to meet the latest showbiz babies, see the most sought after wedding pictures of the year, or take a guided tour around your favourite star’s lavish multi-million pound home – all for free!
“I was heartbroken. I turned the key and drove home.”
Johnny is suing Amber for $50 million (£40 million) over a Washington Post article, where she claimed she was a victim of domestic abuse. She did not name him in the article.
Amber later counter-sued Johnny for $100 million. The actor has already taken the stand and denied ever striking a woman.
For all the latest TV and Showbiz news, sign up to our daily newsletter here.