"Home Alone” star Macaulay Culkin is entangled in a surprising gay scandal after being caught in a grope and steamy makeout session with a male singer!

The shocking clinch occurred toward the end of November, during a performance of Macaulay’s parody rock band “The Pizza Underground” in Billings, Mont. The incident was captured on cell phones and uploaded to the Internet.

Singer Sean Tillman, 36, whose act was opening for Macaulay’s band, was the object of the “Richie Rich” actor’s affection, The National ENQUIRER has learned.

Sean, who goes by the stage name “Har Mar Superstar,” often performs his shows nearly nude, seemingly obsessed with his own sexual prowess.

His “nom de rock” originates from a shopping center, the Har Mar Mall, in Roseville, Minn.

“It’s a shocker,” a friend divulged. “Some people think it’s just part of the act, but Mac seems really into kissing the guy.”

In the video, Macaulay, 34, wore a white T-shirt and loose-fitting floral pants. He sported his usual flaxen hair and sparse beard.

He danced a hustle routine with the balding chubby “Har Mar” – the two facing each other and then taking turns dropping down on their knees.

“Har Mar” then grabbed Macaulay and planted a big, wet kiss on his lips, and dipped him for yet another smooch!

As the two fell to the floor writhing, the audience whipped out their cell phones.

“The Pizza Underground” and “Har Mar Superstar’s” fall “love tour” came to an end in Boston on Dec. 6.

Last month, a rumor went viral that Macaulay was found dead in his New York City apartment. The quirky star quickly posted pictures to prove he was still alive.

In 2012, The ENQUIRER exposed Macaulay in a world exclusive, claiming he was secretly hooked on heroin and was also shooting the dangerous drug Oxycodone.

While his rep denied the claims, the report sent shock waves worldwide.