Gwyneth Paltrow is ''so proud'' of her son Moses.

The 'Iron Man' actress paid tribute to the teenager - her youngest child with ex-husband Chris Martin - to mark his 13th birthday on Monday (08.04.19), and admitted she ''couldn't believe'' he's reached the milestone age already.

Sharing a photo of Moses in action on their current snowboarding vacation, Gwyneth wrote on Instagram: ''Happy birthday my #mosesmartin I simply cannot believe you are THIRTEEN. I am so proud of the man you already are. You steal my heart everyday.(sic)''

The post then received a number of comments from the 46-year-old actress' famous friends, wishing Moses a happy birthday.

Fitness trainer Tracy Anderson wrote: ''Happy Birthday sweet Moses! I completely see how he steals your heart everyday he has always been a heart melting beautiful sweet soul! Have the best day ever! Sam is definitely impressed with the snow boarding and we are all sending you tons of love!!!!! (sic)''

Amanda DeCadenet posted: ''Happy Happy Birthday Mosey (sic)''

Stylist Rachel Zoe was stunned that Moses had reached teenagehood, as she simply wrote: ''OMG 13''

Gwyneth's post isn't the first time Moses' parents have sent him a birthday message so publicly.

Three years ago, his dad - who also has daughter Apple, now 14, with Gwyneth - asked Moses to join him on stage during Coldplay's concert in Lima, Peru.

The 'Hymn For The Weekend' singer was performing with his band in the South American country for their 'A Head Full Of Dreams Tour' and stopped the show to wish his youngest child a happy birthday, three days before the big day.

The 'Avengers' actress was in the crowd and filmed the whole thing on her phone, which she then shared on her Instagram account along with the caption: ''When your dad wishes you an early 10th birthday at work...#coldplaylima (sic)''

In the video, Moses could be seen being escorted on stage before blowing out candles on a cake in front of the packed out auditorium.