1:54 PM PT -- TMZ has obtained some video of Katy Perry's last residency show in Vegas -- and it looks like the stars on hand, including Celine Dion, were busting a move and having a blast.

Check out this footage that shows the celebs who attended boogying down throughout the concert -- you can see Celine Dion bobbing to the music as Katy did her thing ... plus, Cameron Diaz and her husband, Benji Madden, were right behind getting their groove as well. So was Zoe Saldana, BTW -- so yeah, it was a packed house, and star-studded to the max.

As for Meghan Markle and Prince Harry ... we're told they were also seated in the VIP section, but they were in a group of seats that were adjacent to Celine and co., so not really with them.

Their night seemed to be a little more low-key ... with Meghan chatting up a woman she was sitting next to, and PH just kinda sitting there minding his own biz, somewhat aloof. Even when they were seen standing up with the others ... the couple just sorta stood there. 😅

Anyhoo, one other notable sighting ... Katy's fiancé, Orlando Bloom, was obviously in the crowd and he had their daughter perched up on his shoulders and Katy explained how much their child means to her. He also danced with their little girl, Daisy Dove, while mom was onstage.

After the show, Katy and Orlando broke off from everyone else and hit up XS Nightclub at the Wynn and celebrated her last bow with The Chainsmokers. Cool way to go out, no doubt.

Celine Dion is definitely on the comeback trail ... she made her second public appearance in a week at Katy Perry's concert last evening -- and Prince Harry and Meghan Markle were also in the crowd!!!

Celine and her twin sons, Eddy and Nelson, dropped in to catch Katy's performance at Resorts World Theatre in Las Vegas Saturday night -- and she looked absolutely spectacular.

This is great news given her health struggles. As you know, Celine has long been dealing with a debilitating disease called stiff-person syndrome, which causes painful muscle spasms.

On Monday, the iconic singer was seen out for the first time in 3 ½ years, showing up at the T-Mobile Arena for a hockey game between the Vegas Golden Knights and her hometown Montreal Canadiens.

As for Harry and Meghan, the couple arrived apart from Celine and her sons to Katy's concert Saturday. They quickly became the center of attention as fans shot cell phone videos of them.

At one point, Harry and Meghan were pictured near Celine, but it's not clear if they ever got to talk to one another.

Interesting photo, nonetheless. And, it seems like everyone had a terrific time, including Katy’s fiancée, actor Orlando Bloom, and their daughter Daisy Dove.