The beautiful Lord of the Rings actress and boyfriend Dave Gardner welcomed a baby boy on Wednesday, 11 February.
The name hasn't been revealed.
Baby Tyler-Gardner arrived six weeks early and will remain in hospital for now, but a rep told People that the tot is healthy.
The pregnancy was confirmed in September, with Liv later telling Town & Country magazine: "The most fun thing about being pregnant again is having those mum hormones flowing around. You're more present in your body, and it's making me a better mother for Milo."
Liv – who is the daughter of Aerosmith rocker Steven Tyler - has son Milo, ten, from her marriage to ex-husband Royston Langdon.
Football agent Dave – whose best friend is David Beckham – has a son called Grey with ex-wife Davinia Taylor.
The very private couple is believed to have met in early 2014 via mutual friend Kate Moss.
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