Timberlake better stock up on the flowers and candy. Pronto.

Blabbing tabloid insiders say actress Jessica Biel felt “sick to her stomach” after catching a glimpse of her boyfriend of more than a year grinding and gyrating on 20-year-old Barbadian pop star Rihanna as the singers recorded a steamy music video for the songstress’ new single “Rehab.”

“Everyone was gushing about the intense chemistry between Rihanna and Justin,” the National Enquirer reports.

“Jessica also saw pictures from the video set while online and felt sick to her stomach when she saw Rihanna in her skimpy outfits looking incredibly sexy.”