David Foster and Katharine McPhee know that people question their age-defying romance, and they don't care anymore.

"David and Katharine are more serious than they ever have been, and don't care what others around them think," a source told E! News. "David and Katharine have been spending a lot of time together recently and are not afraid to show affection now."

PG / Splash News

On Nov. 30, the two were were spotted after lunch in Los Angeles, and they didn't seem to think twice about sharing a kiss while in full view of paparazzi.

The source added, "David is usually a playboy but Katharine has made him change his ways, and he is really comfortable with her. He tries to fit Katharine into his schedule with dinners and lunches during the week. They both love being out in public together, and are enjoying each other's company. Katharine has always had a crush on David, and she's happy that their relationship is transpiring."

Photographer Group / Splash News

For the better part of the year, romance rumors have surrounded Kat, 33, and David, 68. In March, they attended a tennis match together. They were seen together in April at Barbra Streisand's 75th birthday party. Then, in May, the duo, who are 35 years apart in age, was seen on a romantic dinner date in Malibu, Calif., and it was loaded with PDA.

Then, in October, reports said the two were dating, but "not exclusively."

They are "just keeping things casual," a source told The Blast.

Sounds (and looks) like these two are about as official it gets.