But now the two-year romance is over – leaving even royal watchers surprised.
"Nobody had any idea that this was coming," Ingrid Seward, editor in chief of Majesty magazine, tells PEOPLE. "She was moving into her new flat and getting on with her life. I thought they were very happy together."
So what went wrong?
"Cressida had a hard time dealing with the focus of attention being on her all of the time just because she was Prince Harry's girlfriend – not because she was herself," Seward tells PEOPLE.
Indeed, the 25-year-old Bonas, who stepped out looking fresh and fashionable the day after the news came out, is "very private" and had always struggled with the public nature of her relationship with Harry, 29, friends say.
"She's really low-key, sweet and down-to-earth," a friend who studied with Bonas at the Trinity Laban Conservatoire of Music and Dance told PEOPLE. "She didn't talk about Harry at all. She wasn't like that."
Bonas's half-brother Jacobi Anstruther-Gough-Calthorpe acknowledged how hard she found the intrusion. "It's not something that is easy for anyone – dating a royal or marrying into the family," he said in an interview with the Evening Standard last November. "She's not a tough cookie at all. She's a sensitive, sweet girl."
And of course, sources say, the young blue blood harbors ambitions to be on the stage, having completed a dance degree at Leeds University and then her postgraduate diploma at Trinity Laban Conservatoire.
While Bonas is now reportedly working in marketing, Prince Harry has told friends that the split will allow her to "concentrate on her career."
As Harry and big brother Prince William prepare to head to Memphis, Tenn., for their friend Guy Pelly's wedding on Saturday, Bonas is lying low in London.
A source close to the ex-couple notes that the pair are still "very much the best of friends." Some reports even suggest the separation might be a temporary one – much like the breakup Will and Kate went through in 2007 before getting back together and announcing their engagement in November 2010.
The Daily Telegraph quotes a source saying, "The relationship has certainly at least paused for a breather."
Adds Bonas's college pal, "It takes time for everyone, no matter who they are, and she will be the same."
With reporting by SIMON PERRY and PHIL BOUCHER