Stephen Alderton, 67, from Cambridgeshire, has had the minimum term of his life sentence increased by five years after the Solicitor General referred his sentence as being unduly lenient.
The court heard that Alderton's daughter had separated from Joshua Dunmore and was involved in on going court proceedings.
Two days after a court ruling, Alderton shot and killed Joshua Dunmore in his home.
Alderton then travelled six miles to a neighbouring village where he shot and killed Joshua's father, Gary Dunmore.
Prior to the ruling, Alderton had written in text messages that he would "override any court decision".
The Solicitor General, Robert Courts KC MP, said:
Stephen Alderton's brutal killing spree has ripped apart a family. His despicable acts of violence are deplorable, and I extend my condolences to the Dunmore family.
I welcome the court's decision to extend Alderton's sentence, and hope it sends a clear message that those who commit murder will face the full force of the law.
Alderton received a life sentence with a minimum term of 25 years at Cambridge Crown Court on 23 October 2023 for two counts of murder.
On 23 of January 2024, the Court of Appeal increased Alderton's minimum term to 30 years after it was referred under the Unduly Lenient Sentence scheme.
