The comedian is so smitten with the singer who he recently enjoyed a romantic holiday in Thailand with he has vowed to end his womanising ways.
He said: "I think I'm in love."
When asked about his relationship with Katy, he added: "I don't think I should be drawn on that."
Friends say the 34-year-old British star is keen to keep the romance under wraps so he doesn’t spoil his chances with the brunette beauty.
A friend told Britain’s The Sun newspaper: "Russell has had a crush on Katy for ages and was like an excited schoolboy after they got together.
"He really sees her as an ideal catch and is prepared to stop seeing other girls.
"He doesn't want to talk about it yet as he doesn't want to blow his chances."
Katy, 24, was photographed in London with Russell at the weekend and despite heading to France for Paris Fashion Week, she is keen to return to the presenter’s home.
A source said: "She knows about Russell's reputation but finds him really charming and funny. She's keen to make a go of it."
Katy and Russell were first romantically linked after the MTV Video Music Awards when they were seen kissing at Lady Gaga's after-party at New York nightspot Avenue.
