The 31-year-old actress and 42-year-old actor attended the 2016 Golden Globe Awards, where Alexander presented Oscar Isaac with Best Actor in a Limited TV Series or Movie for "Show Me a Hero."
Alexander turned heads in a black Genny gown with green detail, while Facinelli wore an all-black ensemble.
The actress shared a photo with her beau on Instagram ahead of the ceremony, writing, "My hot date @peterfacinelli #goldenglobes.
Alexander and Facinelli started dating after the actor filed for divorce from Jennie Garth in 2012, and got engaged in March.
He and the "Beverly Hills, 90210" actress share three children: 18-year-old Luca, 13-year-old Lola and 9-year-old Fiona.
"We're just having fun, and we just take life in stride, and we're having fun being engaged and just enjoying life," Alexander told People in May. "[I'm looking forward to] just [spending] every day with him. He's really changed my life. Him and his children have made me a better person."
Olivia Wilde and fiance Jason Sudeikis were among the other happy couples at the awards ceremony. The 31-year-old actress and 40-year-old actor, who got engaged in January 2013, welcomed their first child, son Otis, in April 2014.
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"It is so much fun," the actress said of motherhood on "The Daily Show with Jon Stewart" in February. "It is so funny how it changes your daily life ... It's a balancing act."
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