The 33-year-old singer dated the Backstreet Boys star when she in the pop band - which made lead singer Nicole Scherzinger a global superstar.
Kaya recently took to her Twitter account to allege The Pussycat Dolls were run like a ''prostitution ring'' during her time in the group.
She joined the girl group as a teenager in 2003 and has publicly claimed entertainment executives took advantage of members, alleging they were ''all abused'' and had pressure put on them to ''sleep with whoever they say'' and that she had been warned that if she spoke out she would ''end up dead'' and her career would be ruined.
Now, Kaya has taken to Twitter to allege that Nick, 37, was aware of the abuse she had to endure - a day after he released a statement denying allegations made by former Dream singer Melissa Schuman that he forced her to have sex with him when she was just 18.
On her Twitter account Kaya wrote: ''Nick Carter was my boyfriend while I was in the Pussycat Dolls. He knew about the abuse I endured and did nothing.
''I guess I now know why. Disgusting. Disgraceful. Disgusted in my heart. Especially because he was a victim of abuse himself. Shame on you Nick!
''Nick denies the allegations just like Robin (Antin - Pussycat Dolls founder) denied my abuse. I know all about the truth here. Don't lie Nick. I'm no longer keeping your secrets
''I was vulnerable and in a group which served me abuse daily. Not surprised I fell in love with a predator and had no idea at first.
''Until we had to meet with his attorney for a sexual abuse case he claimed was a fan. Well Nick that was back in 2004 are you gonna deny this?
''Better yet why don't you ask Nick why I left him. Yup he never dumped me, I left him. My heart shattered at what I found out and what he asked me to do! No More Lies!
''I am 33 and not 19 anymore. I like many girls was blinded by evil and I loved him. I'm not scared anymore.
''I've kept a lot in and today after hearing yet another girl was abused can't remain silent. Shame on you Nick for not stopping your sexual demons!
''Nick you have 1 shot to get it right. You can disregard the girls that aren't on your level even after you abused them.
''Come Square up with me the girl that was with you for 2 years that knows all your secrets. Let's go!
''Remember 1 thing when going through pain. No matter how hard or broken you might feel, you are a soldier of God & Soldiers don't cry. Chin up! (sic)''
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