Queensland's attorney-general has applied to the High Court to appeal a decision to reduce the sentence for the juvenile who killed south-east Queensland mother Emma Lovell.

In 2022, the then-17-year-old broke into her North Lakes home on Boxing Day night with another teenager.

He fatally stabbed Ms Lovell in the chest during a struggle with the 41-year-old and her husband Lee on their front lawn.

He was sentenced to 14 years in jail last year after pleading guilty to several offences, including murder.

The 20 year-old's sentence was reduced last month after the Court of Appeal ruled it was manifestly excessive.

His new release date will be in 2031, after serving 60 per cent of his sentence, and he will remain on a supervision order until 2036.

Attorney-General Deb Frecklington said

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