Steven Tyler has become a grandfather for the fourth time

Sharing their news on Instagram, the 38-year-old model wrote: "The love of my life has finally arrived and I am now complete.

"No words can explain how I am feeling. Just pure unfiltered love.

"My son, Axton born on May 10th at 5.45 am (sic)"

There is also a picture of Steven holding the newborn, which the model

captioned: "Best day of my while entire life.

"I'm so grateful for my family and my lover for being here & being so supportive.

"And to the friends and family that came to welcome our new lil wolf cub Ax into the pack.(sic)"

The 69-year-old rocker is also grand parent to his actress daughter Liv Tyler's son Milo Langdon, 12 - whom she has with ex Royston Langdon - and two-year-old son Sailor and 10-month-old daughter Lula Rose Gardner, her children with husband David Gardner.

In March, the 'Crazy' hitmaker posted a picture onto his Instagram account to his 1.1million viewers showing Liv, 39, holding up her baby Lula with son Sailor next to him.

He captioned the image: "If Mama ain't Gappy ... ain't nobody Gappy...

@MissLivalittle's new #Mamasaid campaign makes everyone happy. (sic)"

Liv recently said she was "forever changed" when she had children and admits being a mother has made her more compassionate.

She said: "The reality is far more exciting and beautiful than what you imagine. The moment you lay eyes on that little human you are forever changed. Being a parent yourself helps you to relate to all parents and your parents. It helps you to have more compassion for all parents everywhere."