The 30-year-old 'Toxic' hitmaker and her finances have been under the legal control of dad Jamie since she suffered a breakdown in 2008, but now Jason will be able to have a say on her general wellbeing including where she lives and her medical care.
Her father, together with her lawyer Andrew Wallet, will continue to control her financial and business affairs, and Jamie is said to be pleased about Jason's inclusion.
His lawyer Geraldine Wyle told People Magazine: ''Jamie's thrilled. It's all in the family,'' before clarifying that the request to add Jason came from Britney and not Jamie.
The move could indicate that the wedding - which will be Britney's third - will take place sooner rather than later.
Los Angeles probate attorney Jeffrey S. Cohen, who is not involved in the case, speculated: ''This is a very unusual situation, because generally you don't see conservatees get married.
''This could be a sign that the couple's wedding is around the corner.
''This is probably a compromise between Britney, her father and Trawick to get the marriage off on the right foot.
''Obviously, her future husband needs to have a say in her well being.''
The former Disney star - who has two sons, Sean Preston, six, and five-year-old Jayden with ex-husband Kevin Federline - is also keen to have her conservatorship completely lifted, but that will only happen when doctors feel convinced she is ready to go it alone.
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