Katy Perry and John Mayer are believed to be dating again.

One diner said: "Katy Perry and John Mayer walked in together, arm in arm, and the whole room literally fell silent.

"Even Dimitri Dimitrov -- Hollywood's most famous maitre d', who has seen everything -- and Sunset Tower owner Jeff Klein both stopped mid-sentence when John and Katy arrived, as if they wanted to announce to everyone in Hollywood they are back together."

Other shocked onlookers at the prestigious restaurant included supermodel Naomi Campbell, actresses Scarlett Johansson and Reese Witherspoon, rapper Kid Cudi and 'American Sniper' director, Clint Eastwood.

The 30-year-old pop sensation was believed to be dating super-producer Diplo, but rumours she had reconciled with the 'Paper Doll' hitmaker emerged earlier this week when she was once again spotted dining with the star at a friend's house in Beverly Hills, California, with the 37-year-old singer spending the night at Katy's home.

The pair - who previously duetted on a track titled 'Who You Love', released in December 2013 - reportedly spent the night together following the meal with pals last weekend, with John not leaving the 'Roar' singer's home until 4pm the following day.