The couple exchanged vows in London on Friday, June 28 in front of around 100 guests, including actress Sara Foster and her writer sister Erin Foster, from the groom's second marriage to Rebecca Dyer.
The newlyweds have since jetted off to Naples to enjoy the traditional romantic break, with Katharine posting a sweet photo of herself on her Instagram Story timeline on Sunday, when she was featured cuddling up to her husband while dining at the waterfront Lo Scoglio restaurant.
Katharine also shared video footage from a boat ride the couple had taken along the European coast, where the pair had been on holiday last summer (2018), when David, 69, asked the 35-year-old to become his fifth wife.
The honeymoon news emerges hours after Katharine revealed she would be adopting her husband's last name going forward.
She took to Twitter on Saturday and simply posted, "Introducing Katharine Foster".
The singer/actress wasn't the only one to share her wedding joy with fans online - David also uploaded a picture of his bride beaming in the backseat of their wedding car, wearing her strapless, ivory Zac Posen dress and clutching her bouquet of roses.
He sweetly captioned it, "I'm in the best seat ever!"
Katharine later changed into a strapless blue silk gown for their reception.
The marriage is her second - she divorced Nick Cokas in 2016 after eight years as husband and wife.
Ironically, Foster had been in attendance at their 2008 nuptials, where he played the piano, two years after he produced Katharine's debut single, "Somewhere Over the Rainbow".