Brand told The Sun newspaper in London he developed a crush on Kunis when they co-starred in the 2008 comedy "Forgetting Sarah Marshall," but she wasn't interested because she was in a long-term relationship with former child actor Culkin.
"She's gorgeous. She's so gorgeous," Brand said of Kunis. "I was chatting her up, and got the conversation around to, 'Have you got a boyfriend?' and she went, 'Yeah.'"
The comedian said he was stunned to discover who Kunis was dating.
"So, you know that feeling of 'How long do I have to maintain an interest in this conversation now?' It's 12 seconds. She's talking about her boyfriend 'Mac'. Eventually, she said 'My boyfriend's coming tomorrow.' She was excited -- and when he came it was not 'Mac', it was Macaulay Culkin! He'd got longer. Like a veal calf. Like he'd been grown in a crate. All pale and scared of himself, like a shaved horse. There was a horror about him! Macaulay Culkin! The little lad out of 'Home Alone!' She's [bleeping] him!"