Ryan Reynolds once saved his nephew's life.

Ryan Reynolds (C) Instagram

Ryan Reynolds (C) Instagram

The 40-year-old actor has revealed he once came to the rescue of his relative because he had taken a CPR course with the Red Cross "years ago" and remembered exactly what to do to help.

The 'Deadpool' star shared the news of his heroic moment on Instagram.

Alongside a picture of him clasping at a prosthetic body, whilst he stood beside Viva First Aid's expert Dan, he wrote: "Years ago, I took a CPR course thru the Red Cross. And holy shit, I ended up saving my nephew's life because I knew what to do! True story! (sic)."

And the Canadian hunk - who has daughters James, two, and nine-month-old Ines with his wife Blake Lively - has since taken a "refresher course" to update his knowledge of infant and toddler CPR.

The post continued: "Yesterday I took a refresher course -- focusing on infant and toddler CPR. It takes only a few hours and it's also kinda, sorta fun. Thank you to Dan from Viva First Aid for the lesson. And thank you to these two helpful yet lifeless dolls whose vacant ocular cavities will haunt me until end times. (sic)."

Ryan was also joined by his 29-year-old spouse, who also took part in the session.

And the former 'Gossip Girl' star has urged "all mamas and daddies out there" to sign up to a class to gain the vital knowledge, and to also get a "piece of mind".

Alongside a photograph of the golden-haired beauty sitting on the floor beside the equipment, which was shared on her photo-sharing site, she wrote: "ALL MAMAS AND DADDIES OUT THERE-- I can't recommend this enough, I took a CPR class with with a focus on babies and toddlers. Google "infant CPR class near me" and you'll see lots of listings. For those of you who haven't done it, you will love it. It's so helpful by giving you knowledge, tools, and some peace of mind. (sic)."