• Mr Asghari, a 27-year-old personal trainer and actor, was born in the Iranian capital Tehran but moved to Los Angeles at the age of 12.
• The couple met on the set of a music video in 2016.
Britney Spears has announced her engagement to her long-term boyfriend, Sam Asghari.
The singer posted a video of the couple showing off the ring on Instagram.
Spears is fighting a legal battle to end her 13-year conservatorship, which controls both her personal life and finances.
She revealed that the terms of the arrangement were preventing her from marrying Mr Asghari or having more children.
The conservatorship arrangement was imposed in 2008 when concerns were raised over the singer's mental health.
Mr Asghari posted a separate photo of the ring and the couple kissing.
His manager, Brandon Cohen, confirmed news of the engagement to People magazine.
"The couple made their long-standing relationship official today and are deeply touched by the support, dedication and love expressed to them," he said.
The couple met on the set of a music video in 2016.
Mr Asghari, a 27-year-old personal trainer and actor, was born in the Iranian capital Tehran but moved to Los Angeles at the age of 12.
In an interview with Forbes earlier this year, he described arriving in the US without speaking any English: "It was definitely a culture shock, coming out here with a completely different language to speak."
Spears, 39, has been married twice before. In 2004, she wed her childhood friend Jason Alexander in Las Vegas but the marriage was soon annulled.
Later the same year, she married dancer Kevin Federline, with whom she has two children. The couple divorced in 2007.
Last week, the singer's father Jamie Spears filed papers in a Los Angeles court to end the conservatorship. She had sought to remove him from the role twice in the last two years.
Britney Spears has previously referred to her father's treatment of her as "cruelty". In July, she told a judge that she wished to file charges against her father for "conservator abuse".
The court-ordered conservatorship gave Jamie Spears control over his daughter's estate and other aspects of her life. Mr Spears stepped down as the conservator of his daughter's personal affairs in 2019 due to health issues, but continued to oversee her business arrangements.