The pair attended the Parker Institute for Cancer Immunotherapy Launch in Los Angeles on Wednesday. The star-studded soiree was held at Napster co-founder and Silicon Valley entrepreneur Sean Parker's home with a guest list that included Bradley Cooper, Minka Kelly, Emilia Clarke, Katie Couric, Sean Penn, Tom Hanks and Goldie Hawn.
Although Perry, 31, and Bloom, 39, walked the red carpet separately, the duo acted very much a couple inside the event.
"They were sitting next to each other," a source tells PEOPLE. "Bloom had his arm sweetly draped around Perry's chair as they chatted with Allison Williams. The pair seemed to be in a great mood."
Parker announced on Wednesday that he will donate $250 million to establish the Parker Institute for Cancer Immunotherapy, which will join together 300 researchers from Memorial Sloan Kettering, Stanford Medicine, UCLA, UC San Francisco, MD Anderson and Penn, according to Reuters. The institutions aims to fight cancer cells by triggering the immune system's ability to seek out and destroy invaders.
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The singer and her rumored beau were first linked in January at a Golden Globes after-party, and in February, Perry was first introduced to Bloom's 5-year-old son Flynn, whose mother is Miranda Kerr.
Most recently, Perry and Bloom were spotted walking arm-in-arm during their weekend getaway in Aspen, Colorado.
Reporting by MARIAH HAAS