“They ordered wagyu and fries. It was a girls’ dinner and they were all super chill and just relaxing and very low-key in the dining room,” an onlooker tells PEOPLE.

In photos obtained by the Daily Mail, the group, which included Lyndsey Bell, wife of Chiefs tight end Blake Bell, was photographed leaving their laid-back dinner dressed in stylish ensembles, including all-black looks for the “Blank Space” singer and Brittany.

Swift, who is dating Kansas City Chiefs tight end Travis Kelce, wore a polo neck sweater and high-waisted mini skirt with lace-up thigh-high boots, along with her signature red lipstick.

Brittany, meanwhile, wore a v-neck sweater tucked into a high-waisted Gucci monogram-print skirt and heeled boots, while pregnant Bell showcased her growing baby bump in a white ribbed dress that she teamed with a black leather jacket and cowboy boots.

The singer and Mahomes’ wife also hung out together on Dec. 17 as they cheered on their other halves at the Chiefs game against the New England Patriots at Gillette Stadium in Massachusetts.

More recently, Swift was seen supporting boyfriend Kelce, 34, again from the stands during his New Year’s Eve game last Sunday, as his team beat the Cincinnati Bengals. The singer rocked a custom Kansas City Chiefs bomber designed by Jeff Hamilton, at the game matching Kelce’s Chiefs jacket he wore on Christmas day.

Swift — who was first publicly romantically linked to Kelce in September — was spotted later that night sharing a kiss with Kelce as they welcomed in the new year in footage captured by an onlooker at a Kansas City party, posted on social media.

In the clip, Swift had changed her casual look for a glamorous sparkly dress by designer Clio Peppiatt, who also designed 34th birthday dress, while Kelce sported a maroon suit.

Last month, Swift discussed her relationship with Kelce for the first time in Time magazine.

The “Anti-Hero” singer told the outlet that their connection “all started when Travis very adorably put me on blast on his podcast, which I thought was metal as hell.”

“We started hanging out right after that. So we actually had a significant amount of time that no one knew, which I’m grateful for, because we got to get to know each other,” revealed Swift.