The British comedian – who has been linked to a string of beauties in the past and is known for his womanising ways – has amazed friends with his new attitude to romance and pals are convinced he is getting ready to ask the singer to marry him.
A source close to Russell said: "We've never seen him like this. He always has a woman on his arm, or in his bed, and hasn't been interested in monogamy.
"But this is different - we all think it won't be long before he marries Katy. I'm waiting for a call to say they are in that Little Chapel in Vegas and have run off to get married."
Former Oasis rocker Noel Gallagher added: "He's a changed man, Russell."
The 34-year-old 'Forgetting Sarah Marshall’ star admitted he has never been happier than since he embarked on his romance with Katy, 25.
He said: "To be honest I haven't stopped smiling. She's a lovely girl and it's going really, really well. In fact I've never felt more settled in all my life. Katy is fantastic. I'm really happy."
Earlier this week Russell – who was first romantically linked to Katy at the MTV Video Music Awards in September – admitted he was ready to settle down and start a family.
He said: "I am ready for children actually. It's been seven years since I took drugs. I've made a film. I don't have to fight so much. I've grown weary of the carousel."
