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During a Monday appearance on The Ellen DeGeneres Show, single mom Hilary Duff opened up about her Ghostbusters-obsessed son Luca, 4.

“He wants to be a Ghostbuster this year,” she said of her son’s Halloween costume. “He’s obsessed with Ghostbusters, obsessed with Slimer. He learned the whole song…it’s so good. He’s so serious about it, you guys.”

In July, the Lizzie McGuire alum, 29, shared a cute clip of her preschooler singing the Ghostbusters theme song.

Then, Ellen presented the actress with a custom Ecto-1 made for the tot, complete with real steam flowing out of it.

“He’s going to freak out!” Duff said. “Do I fit in this thing? It has steam coming out of it! He’s going to lose his mind.”