Alan Thicke's older sons, Brennan and Robin Thicke, are gearing up for a court battle with the late actor's third wife, Tanya Callau.
Brennan and Robin -- who are co-trustees of Alan's living trust -- filed a petition on Tuesday asking the court to rule on the validity of the living trust, claiming that they had no other choice but to do so in order to "honor the memory of their father, protect his legacy, and prevent his testamentary intentions from being undermined by avarice and overreaching of ... Callau, now that Alan is unable to defend against her claims." Alan's sons claim Tanya is now insisting that the prenuptial agreement she signed before marrying the late actor in 2005 is invalid, though they claim she had made no complaints about the prenup or Alan's estate plan when he continually updated his trust -- the last time being in February 2016 -- before his death last December.
Alan's sons also claim through their attorney that Tanya has threatened them with bad press unless they agreed to "participate in a mediation and succumb to her demands."
WATCH: EXCLUSIVE: Inside Alan Thicke's Wedding to Tanya Callau and a Look Back at Their Love Story
According to court documents, Alan left each of his three children -- including 17-year-old Carter -- equal shares of his ranch in Carpinteria, California, 75 percent of his personal effects and 60 percent of his remaining estate, Meanwhile, he left Tanya with the ranch's furnishings, 25 percent of his personal effects, a $500,000 life insurance policy, all of his death benefits from pensions and union memberships and 40 percent of his remaining estate. Alan also provided that she could live at the ranch, as long as she paid for its expenses and maintained the property.
"Nonetheless, despite Alan's generous benefits and careful planning Tanya demands more," the petition claims. "Now that Alan is dead, Tanya claims there are numerous problems with the Trust and the Prenuptial Agreement. Tanya asserts that there is no chance the 'Prenup' could withstand legal challenge and that she has very significant community rights in the Trust’s assets and rights of reimbursement with respect to improvements to the Ranch."
"Tanya also claims 'Marvin rights' asserting that she had to forego opportunities to pursue and advance her own career in order to support Alan and be his companion and partner, including raising Carter," the petition claims.
Brennan, 42, and Robin, 40, are now asking the court for instructions concerning the extent to which the Trust's property is Alan's separate property, and whether Tanya's challenge to the prenup is invalid because she signed it.
Brennan and Robin's lawyer, Alex Weingarten, said in a statement to ET on Tuesday that the court filing was a last resort for his clients.
"My clients made every effort to resolve this without the need for going to court," Wengarten says. "The only thing they care about is protecting the legacy of their father and honoring his intentions. That is exactly what we are going to do."
Alan died in December shortly after he collapsed while playing hockey with his son, Carter, and suffered a ruptured aorta. He was 69 years old.
A source close to the family told ET at the time that Tanya was "beside herself" with grief after the Growing Pains star's death, and that Robin "really stepped up" to plan his star-studded memorial service.
WATCH: Alan Thicke's Wife Tanya Shared Moving Photo of the Couple Two Days Before His Death
ET was at Alan and Tanya's family-oriented 2005 wedding in Cabo San Lucas, Mexico. Carter, who was only seven years old at the time, served as the ring bearer, while Robin serenaded the newlyweds at the reception with Al Green's "Let's Stay Together."
Watch the video below to see the family in happier times.