The basketball star, who shares three-year-old daughter True with the Kardashian sister, said he was ‘so incredibly sorry for his actions in a social media post that addressed her directly.
Their relationship has been on-off and a cheating scandal involving Thompson featured in later seasons of Keeping Up With The Kardashians.
‘Today, paternity test results revealed that I fathered a child with Maralee Nichols,’ he wrote in a statement shared on his Instagram story.
‘I take full responsibility for my actions. Now that paternity has been established I look forward to amicably raising our son.
‘I sincerely apologize to everyone I’ve hurt or disappointed throughout this ordeal both publicly and privately.’
He continued: ‘Khloe, you don’t deserve the heartache and humiliation my actions have caused you.
‘You don’t deserve the way I have treated you over the years. My actions certainly have not lined up with the way I view you.
‘I have the utmost respect and love for you. Regardless of what you may think. Again, I am so incredibly sorry.’
Last month, Maralee, who welcomed a son at the start of December, spoke out on her secret relationship with Tristan after his paternity test was dismissed in Texas.