"Kevin is very happy for Britney and wishes both she and Sam a happy and full future together," Kaplan says. "It would seem to indicate that positive things are going forward for her as she takes more control of her life."
Spears and Federline were married from 2004 to 2007 and share two children together; sons Sean, who turns 16 on Tuesday, and Jayden, 15.
In a previous statement to ET, Kaplan said Federline also supported Spears' efforts to end her conservatorship. Months after Spears spoke out in court, her father, Jamie Spears, filed documents to officially end her 13-year conservatorship.
"What is best for her, Kevin supports her in being able to do that," Kaplan said in June. "It doesn't matter how positive of an effect a conservatorship has had if it's having a deleterious effect and detrimental effect on her state of mind. So he supports her having the best environment for her to live in and for his children to visit with their mother in."
Spears has been in a conservatorship since 2008, when her kids were just toddlers. Now, as teenagers, Kaplan stated that "Kevin feels that the best thing for his children is for their mother to be happy and healthy."
As for the new engagement, Spears and Asghari shared the news with fans on Sunday.
"I can’t f**king believe it 💍💍💍💍💍💍❣️!!!!!!" Spears wrote on Instagram, as fans shared their well wishes for the couple in the comments.
On Monday, Asghari thanked fans for their support, and addressed concerns about protecting Spears' finances.
"Thank you everyone who is concerned about The prenup!" he wrote on his Instagram Story. "Of course we're getting [an] iron clad prenup to protect my jeep and shoe collection incase [sic] she dumps me one day."