Anna Kendrick, Justin Timberlake & Daniel Radcliffe cringe listening to Robbie Williams' sex story

Robbie Williams just left Anna Kendrick, Justin Timberlake and Daniel Radcliffe totally gobsmacked.

The English singer and the three Hollywood stars appeared on "The Graham Norton Show" and Williams left the entire group with their jaws on the floor when he regaled them with the wackiest, wildest sex story of all time.

Norton had asked a simple question, "What's the maddest thing a fan has given you?"

At first Williams quipped back, "Herpes" leading the group to roll with laughter and Timberlake to try and walk off the set. Honestly, we're pretty sure the "Sexy Back" star was gonna lose it.

Then, after telling Norton that "you can't get herpes twice," Williams decided to tell the whole group a story about how he was once in a castle and got a very pleasing gift from a fan.

[WARNING: Graphic story below]

"I can't believe I'm telling this but I will. Back in the day, I was renting a castle, that's my life. We were renting to rehearse in for a tour. I was in this big room, I had gone to sleep, I woke up and I was lying in my bed and I was cognizant and I was awake but I hadn't opened my eyes yet," he explained. "I was getting more and more confused because I could swear there was somebody in my room and I could swear that they were sort of tidying up or cleaning or something. I open my eyes and there was a lady at the end of my bed. She could have been anywhere from 28 to 58."

"I was like, wow, this situation is really odd. But you just woke up, so you don't really know what's going on. She looks at me, I look at her and I went 'Alright,' she went 'Alright.'"

Here's where the dirty details really start.

"She went, 'Have you got morning glory?'" Williams explained, a British colloquialism for ... well, you can probably figure it out. "This was back in the day when I used to have morning glory. I was like, 'Yeah.' She says, 'I'll wank you off.'"

Timberlake literally couldn't contain himself with laughter. And Kendrick just couldn't stop putting her hand over her mouth. She looked beyond embarrassed by the story. Their reactions are completely priceless.

PHOTOS: Robbie Williams through the years

"She does the dirty deed and it's confusing and I felt defiled and off she went on her merry way," he continued. "That night, I was with the lady who ran the castle and said, 'Your cleaner's weird.' She said, 'We don't have cleaners on Wednesday' It was just somebody who had walked in off the street with a feather duster, come up and gave me a hand job and then left!"

"That's the best thing, we can all go home now, that's the best story of the day," Radcliffe joked after Williams was done, as everyone on the couch broke out into laughter.

Watch the cringe-worthy interview above.