Tristan Thompson allegedly knew that he was expecting a baby with another woman whilst he was in the process of having a child via surrogate with Khloé Kardashian.
The basketball player, 31, and the reality TV star, 38 - who were already parents to daughter True Thompson, four - welcomed a son, born through surrogacy, last month.
He had previously welcomed a son, Theo, now 9 months old, with Maralee Nichols in December last year, having slept with her whilst he was allegedly still dating Khloé.
Khloé has claimed in the season two debut of the Kardashians that Tristan knew about Maralee's pregnancy whilst they were planning to welcome a second child together.
She alleges that he knew that Maralee was pregnant in July last year, which she claims was several months before their own surrogate was impregnated in November.
Khloé also suggested that Tristan was keen to have their second child by a certain date, with the implication being that he was already aware of when Maralee was due.
"All I know is I was being encouraged to do it by a certain date. In hindsight, he always knew when the other baby was being born," she commented in the season two opener.
Khloé added that paperwork she had allegedly seen suggested that he found out by early July last year, with her saying during an emotional segment: "So he did know".
She said it was just before Thanksgiving, in late November, that they had an embryo transfer and that it was in early December that she heard about Maralee's pregnancy.
Khloé asserted in the episode that she wouldn't have agreed to the surrogacy had she known that Tristan was expecting a child with another woman at that time.
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She said: "Why would I want to have a baby with someone who's having a baby with somebody else? I'm not that much of a sociopath. I'm a lunatic, but not like that f***ing deranged."
The allegation left some of her relatives unimpressed, with younger sister Kendall Jenner, 26, speculating that it seems as though Tristan wanted to "trap" Khloé with their baby.
She commented: "That's what's wild. You were encouraging Khloé to go forward with this while you knew that this was also happening? It's almost like he wanted to trap her."
The Mirror approached Tristan's rep for comment.
The second season of the Kardashians launched on Disney Plus in the UK earlier today (September 22). New episodes will be released each Thursday and you can catch up now.
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