According to The Sun, the make-up artist was reportedly at her father's side at her family home, in Oxford with her mum Linda, when he passed.
It was also reported that Derek was discharged from hospital in recent weeks, so that he could die at home peacefully.
Last year, Lisa Armstrong split from her husband of 12 years, Ant McPartlin.
The Britain's Got Talent host and Lisa had been together for 23 years, having first met in Newcastle in 1994.
They went onto exchange vows at a stunning country house in Buckinghamshire, in 2006, and announced their split in January last year.
Things haven't been easy for Lisa, but she really has taken everything in her stride.
Our thoughts are with her, and her entire family at this tough time.