Alleged triple killer, Jordan Monaghan, 30, is accused of smothering his daughter, Ruby, aged 24 days, on New Year's Day, 2013, eight months before also smothering his son, Logan, aged 21 months.
He also denies the murder of his new partner, Evie Adams, 23, six years later in October 2019, by giving her an overdose of tramadol and diazepam.
At the start of the second week of the trial at Preston Crown Court, the jury heard from Laura Gray, 28, the mother of Ruby and Logan, and Monaghan's partner at the time.
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Ms Gray said hours before Ruby died she and the defendant had put Logan to bed and watched the TV, her daughter had fed normally and was "absolutely fine".
After seeing in the new year, she went to bed just after midnight with Ruby sleeping in her Moses basket on the living room floor.
For the first time, Monaghan offered to stay up to give Ruby her 2am feed. But she was awoken shortly before 2am by her partner shouting from downstairs.
Ms Gray told the jury: "He shouted, 'Laura, come down now. I don't think Ruby is breathing'."
Duncan Smith QC, prosecuting, asked the witness: "How did Ruby look to you?"
Ms Gray replied: "She looked grey and her lips were blue. She felt clammy.
"I could not see her breathing.”
An ambulance was called and rushed the child to hospital accompanied by her mother, but she did not regain consciousness and despite emergency treatment Ruby was pronounced dead at 2.45am.
Ms Gray asked a nurse to call Monaghan, before he arrived at the hospital, but not to tell him their daughter had died.
However, when he got there and Ms Gray told him their daughter was dead, he replied, "I know, I know" saying a nurse had told him on the phone.
But the jury heard none of the hospital staff made such a call to tell him.
Monaghan, of Belgrave Close, Blackburn, denies three counts of murder, two counts of attempted murder and two counts of cruelty to a third child, who cannot be identified, all between January 1, 2013 and October 24, 2019.
The trial was adjourned until Tuesday morning.
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