'Baby One More Time' singer Britney met Justin when they were kids, working together on Disney show The New Mickey Mouse Club. (She later revealed her first kiss had been with Justin at 13.) Friendship turned into romance and they dated between 2000 and 2002.
And in a new interview with USA Today, Britney, now 32, showed she's still of supportive of her ex, naming him alongside artists like Bruno Mars and Lorde as bringing something new to the music industry.
"This generation is hungry for new sounds. Bruno Mars is so different and fresh, and Justin Timberlake is, too. It's inspiring for me, and it makes people eager to listen to music, which helps everyone," she said.
Britney also namechecked Beyonce and Michael Jackson as inspirations.
The pop star kicked off her two-year Las Vegas residency at the Planet Hollywood Resort and Casino on 27 December and, showing she's also inspiring other artists, she played to a sold-out crowd that included Miley Cyrus, Katy Perry and Adam Lambert.
Miley tweeted: "If u told me I'd be front row & centre on @britneyspears opening night 10 years ago I wouldve never believed you." She later added that "dreams do come true."
Katy said: "Soy excited to see @britneyspears baby bottle pop it off tonight at her grand opening @phvegas! We are coming in full lewks to support! (sic)."
Britney replied to both singers via Twitter. She told Miley: "Love you so much! Thank you for coming to #PieceOfMe! I adore you :)" To Katy, she wrote: "Was SOOOO good to see you again girl! Glad we could make our Vegas date happen :)."
Her show, Britney: Piece Of Me, features more than 20 of her greatest hits and will run for 50 dates across a two-year period.
Britney Spears' changing looks through the years - gallery:
Copyright: Britney Spears / VEVO
Listen to Britney's new song 'Perfume' below: