The 37-year-old actress took to Instagram on Saturday (07Jan17) with an open letter to her son, who had turned 13. Captioning a snap of her holding hands on the beach with Ryder as a toddler, she began her lengthy message by calling herself lucky.

"Thirteen years... Today I reflect on how lucky I am to have spent my entire adult years being Ryder’s mother,” she wrote. "My dear Ryd man! Today you are 13! Hard to believe but I’m staring right at you and my goodness yes you are a teenager! I couldn’t be more in love with who you are as a person and who you are growing into as a young man.

"Smart, funny, joyful, tolerant, perceptive, empathetic, loving, you continue to maintain the beautiful attributes of your true nature and I will always be there as your touchstone to help nurture them or rediscover them if they ever get cloudy," Kate continued. "But watching you independently keep these characteristics close and alive has been a wondrous journey in which I look forward to witnessing every waking hour. Happy Birthday baby!!! 13 is looking pretty awesome so far!!! I love you #RyderIsThirteen #HappyBirthday #ProudMama.”

The actress shares Ryder with Chris Robinson, frontman of The Black Crowes. The couple wed in 2000 in Colorado, but split in 2007. Kate has another son, Bingham Hawn Bellamy, who was born in 2011. She split with Bing's father, Muse rocker Matt Bellamy, in 2014.

However, the Almost Famous star has remained friends with both her exes, and even spent Christmas with Matt and his girlfriend Elle Evans at her family ranch in Colorado.