A spokeswoman Monday confirmed Hughes proposed to Holden two weeks ago, although no wedding date is set, Britain's Daily Mail reported Tuesday.
The groom-to-be reportedly gave his fiancee a $35,000 diamond ring.
Holden and Hughes, who have been friends for 10 years, started seeing one another after Holden split from Dennis. They have lived together in southwest London for the past year, the Daily Mail said.
"It's the most amazing love I've ever experienced. Having a family is important to me and knowing that Chris will make an amazing dad is a comforting thought," Holden told the newspaper.
The 32-year-old actress is set to star in an ITV adaptation of "Miss Marples."