Who was Donna catch David kissing in a beach house on ';Beverly Hills 90210';?

In the series, Donna and David break up and the interloper tries to mediate the situation by saying ';all they did was kiss';. Donna's response is, ';That's all we do.';Who was Donna catch David kissing in a beach house on ';Beverly Hills 90210';?
thats in season 3 when donna goes to london with brenda and david makes out with nikki at the beach club.

skin deep