United Kingdom, Sept. 15 -- Katy Perry and Justin Trudeau are still "very interested in each other".

The 40-year-old pop star and the former Canadian Prime Minister are still quietly seeing each other - but they're now making a concerted effort to keep their burgeoning romance lowkey.

A source told Us Weekly: "They've decided to be much more private about it.

"They are still speaking and are very interested in each other."

By contrast, another source suggested that their relationship "isn't serious" at the moment, adding that Katy is "extremely busy right now" with her Lifetimes Tour.

The insider shared: "Justin has made plans to see her when she has downtime in a few weeks when she gets back from her tour in Brazil. Katy is taking i...