Both Kristen and Stella, who were reportedly in high profile relationships with St Vincent and Miley Cyrus respectively, were enjoying a low-key holiday in Italy where Maxwell was walking during Men's Fashion Week.
Stella hit the runway for a number of shows including Dsquared2 and Moschino and was joined by her other half as they soaked up the atmosphere for a few days before jetting back to the US.
Stewart, whose relationship with former Twilight co-star Robert Pattinson was young Hollywood's version of Brangelina, said she finally decided to go public with her romance with now ex-girlfriend Alicia Cargile.
"When I was dating a guy I was hiding everything that I did because everything personal felt like it was immediately trivialised, so I didn't like it. We were turned into these characters and placed into this ridiculous comic book, and I was like, ‘That’s mine. You’re making my relationship something that it’s not.’ I didn’t like that," she explained.
"But then it changed when I started dating a girl. I was like, ‘Actually, to hide this provides the implication that I’m not down with it or I’m ashamed of it, so I had to alter how I approached being in public.
The daughter of Northern Ireland diplomat Maurice Maxwell and Stella Maynes, Stella was born in Belgium and has spent most of her life abroad.
She began her modelling career while studying as a student in New Zealand.
Her father Maurice, a graduate of Queen's University, Belfast, worked for the European Commission and spent many years in Brussels.
Mr Maxwell's most recent appointment before retiring in 2012 was as head of the European Commission's office in Belfast.
Stella Maxwell debuted her Angel wings - a career high for any model - at the Victoria's Secret annual fashion extravaganza in the US in 2014.