Though she hasn't yet congratulated him herself, the star told E! News at Wednesday's Barbershop: The Next Cut premiere in Los Angeles that she is "so happy" for her ex.
"I think everybody deserves happiness and I think it's just absolutely awesome," she added. "He looks like he's so happy."
The former Cheetah Girl, 32, dated Kardashian, 29, from 2007-09.
On Monday evening, Kardashian popped the question to model/business owner Chyna, 27, just 10 weeks after the two went public with their relationship.
While the newly engaged happy couple hasn't been shy about showing off their love and the 7-carat sparkler, Kardashian's family has remained silent about the news on social media.
A source told PEOPLE Thursday that sister Khloé Kardashian in particular feels "betrayed" and is "furious at the lack of respect." (Her brother's engagement to Chyna – who has a tense history with the famous family – took place while the entire Kardashian-Jenner crew was on vacation in Vail, Colorado.)
"Khloé plans on ignoring the news. She is not going to send Rob any well wishes," revealed the insider. "She is not happy about the engagement, and is not going to pretend that she is."