The 20-year-old actor, who plays Jennifer's fake son Kenny in the film, attended the UK premiere on Wednesday night and spoke to HELLO! Online about the experience.
CLICK ON PHOTO FOR GALLERY
"It's the most bizarre scene in film history," said Will. "Rose, the fake mum, and Casey, the fake sister, teach fake son Kenny how to kiss, and then fake dad David comes in and eats crisps and watches.
"It was the weirdest, most awkward thing to shoot. I'm guessing Kenny loved it though."
While many men can only dream of getting up close and personal to the Hollywood beauty, Will seems to have blocked the scene from his memory and can't recall how many takes it took.
"I really can't remember," he said. "It was all a scary blur."
Will also joked that Jennifer's actor fiancé Justin Theroux had not given him any tips beforehand.
The young actor, who found fame as Eustace Scrubb in The Chronicles of Narnia: The Voyage of the Dawn Treader, spoke highly of his Hollywood co-star.
"Jennifer's a phenomenal actress," he said. "It was so nice to find out what a lovely person she was. Despite all the fame, she' stayed so true to herself. It's fantastic."