"She was nervous about being spotted and entered quickly trying to cover up. Orlando opened the door for her. They were holding hands in the car. They each rested their arms on the centre console and they were definitely interlocked."
The news comes after the pair were first spotted "aggressively flirting" at a post-Golden Globes party back in January.
A source said at the time: "Katy and Orlando were standing in the back of the party drinking Moët and were aggressively flirting before leaving together.
"He wouldn't stop staring at her cleavage - and she was very flirty and laid on the charm.
"He would lean in to whisper into her ear and touch the small of her back as they chatted."
And just weeks later, they attended a one-man show, The Absolute Brightness of Leonard Palkey, together.
Katy was previously married to Russell Brand and was most recently in an on/off relationship with singer John Mayer, while Orlando has a 5-year-old son, Flynn, with ex-wife Miranda Kerr.
- Bang! Showbiz