Details behind Reese Witherspoon's shock split from husband of 12 years Jim Toth

Reese Witherspoon and her husband of 12 years Jim Toth's marriage broke down because of "irreconcilable differences" – or so their divorce filing claims.

The Legally Blonde star has officially filed to divorce from her former talent agent husband and the document states there is a prenuptial agreement in place, People reports.

Witherspoon, 47, cited "irreconcilable differences" and has asked the court to designate both her and Toth as the joint custodians of their 10-year-old son, Tennessee.

READ MORE: Chris Hemsworth reportedly taking a step back from acting after health revelation

READ MORE: Oasis reunion rumours swirl as sources claim Gallagher brothers are healing relationship

The former couple reportedly signed a prenup agreement in March 2011 which will "provide adequate and sufficient provisions for their assets and debts".'

They will also have to register for a parenting class and have 60 days to submit a certificate of completion to the court.

Witherspoon took to Instagram on March 24 to announce she was splitting from Toth, just days before they were due to celebrate their 12-year anniversary.

"We have some personal news to share..." their joint statement began. "It is with a great deal of care and consideration that we have made the difficult decision to divorce. 

"We have enjoyed so many wonderful years together and are moving forward with deep love, kindness and mutual respect for everything we have created together."

The couple said their "biggest priority" is their son, Tennessee, and the rest of their family as they navigate the next chapter of their lives.

READ MORE: 'Overjoyed' Big Bang Theory star welcomes her first child

"These matters are never easy and are extremely personal. We truly appreciate everyone's respect for our family's privacy at this time."

A source told People things remain amicable between the former couple following their announcement, claiming Witherspoon and Toth are "the best of friends".

"This is such an amicable decision. They are so committed to co-parenting together. They are invested in their whole family and making this as smooth as possible for everyone," the insider claimed.

The exact reasons behind their split remain unclear, however another insider said the couple had been spending very little time together due to Witherspoon's busy acting schedule.

"They've been spending less and less time together while she was working," the source added.

Page Six also reported the couple's marriage ended because it had grown platonic and there was "zero romance" left.

READ MORE: 'I'm feeling a bit sick': Inside the most awkward Aussie TV moment of all time

"There's no big scandal or drama, just two people who essentially became co-parents and don't really have any romantic feelings for each other anymore," an insider told the publication.

Witherspoon and Toth married in March 2011 and welcomed their son Tennessee in 2012.

The Cruel Intentions actress also shares daughter Ava, 23, and Deacon, 19, with ex Ryan Phillippe.