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Canadian pop star Justin Bieber released his first solo single in four years on Friday, kicking off a career comeback that will see him release a new album, go on tour and star in a documentary series this year.

The 25-year-old, who found fame as a baby-faced teenager, told fans last month he would release his fifth studio album in 2020, his first since 2015’s Purpose.

Bieber’s new R&B single 'Yummy' appears to pay tribute to his model wife Hailey Baldwin, whom he married for a second time last year, with lyrics such as “I’m elated that you are my lady” and “You got that yummy-yum”.

Bieber, who pulled out of his 2017 Purpose world tour saying he needed rest, last year took to Instagram to talk about his struggles with “deep-rooted issues” saying he was putting new music on hold.

“As humans we are imperfect. My past, my mistakes, all the things that I’ve been through, I believe that I’m right where I’m supposed to be and God has me right where he wants me,” Bieber said in a video last week, in which he also listed dates for a North American tour.

“I feel like this is different than the previous albums just because of where I’m at in my life.”

While 'Yummy' is his first solo single in a while, Bieber has collaborated with others, including DJ Khaled and Ed Sheeran, on different records in the last few years.

Earlier this week, YouTube - where Bieber first found fame as a 13-year-old - said a 10-part documentary series Justin Bieber: Seasons, in which the 'Baby' and 'Sorry' singer talks about his new album and personal life, would launch on the video platform on Jan. 27.