Rod Stewart and son Alastair look so alike as they celebrate special milestone

Rod Stewart performing in a yellow suit
(Lora Olive/ZUMA Press Wire/Shutterstock)

Rod Stewart had a moment of celebration during the week as the rock and roll legend celebrated his son Alastair's 18th birthday. The star shares sons Alastair, 18, and Aiden, 13, with his current wife Penny Lancaster.

Taking to his Instagram Stories, Rod shared a photo alongside his young son, and they looked so alike! In the stunning snap the pair were captured in a restaurant sitting next to each other and beaming for the camera. Rod was dressed in his signature style with a flamboyant red jacket, while Alastair opted for a white jumper, while also slicking his hair back.

Making a reference to their shared love of Celtic Football Club, the 78-year-old commented: "Celtic Brothers," alongside his post as well as tagging his son, and adding a sticker that read 'Happy birthday'.

The teenager shared some insights into his birthday meal with his family, revealing that his half-sister Renee was also in attendance. The model also tucked into a delicious-looking chocolate cake that would have left the Great British Bake Off judges salivating.

Alastair and Rod Stewart sat at a restaurant
The father and son looked so alike! (Instagram)

Alastair's mum, Penny Lancaster, also got in on the celebration and on her son's big day, she uploaded a carousel of touching snapshots from her son's childhood. Amongst the images, former Loose Women star Penny made sure to include a heart-melting baby photo.

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In the precious image, Penny and her husband Rod Stewart are pictured beaming from ear to ear alongside their tiny tot. The family trio donned neutral outfits with Penny rocking a lace-trimmed cardigan, and Rod wearing a crisp white shirt. A young Alastair, meanwhile, is pictured front and centre of the image wearing a simple white baby grow.

A slice of a chocolate cake
Alastair marked his birthday with a delicious cake (Instagram)

Over on her Instagram Stories, Penny also uploaded a more recent selfie featuring her teen son. The TV star looked every inch the proud mother as her lookalike son towered over her wearing a leather bomber jacket and pair of stylish sunglasses.

Alongside her string of photos, Penny gushed: "My beautiful first born son that I had dreamt of for 34 years of my life, came to me as a gift that I have always treasured [heart emoji] happy 18th birthday. So proud of the wonderful man you have become xxxx @alastairwstewart."

Penny Lancaster in green dress and Rod Stewart in suit
Rod shares Alastair and son Aiden with wife Penny Lancaster (Richard Young/Shutterstock)

Alongside the sons he shares with Penny, Rod is also a devoted father to Sarah, Kimberly, Sean, Ruby, Renee and Liam, with his eldest being born in 1963. The musician shares his children with a variety of partners including ex-girlfriend Susannah Boffey, ex-wives Alana Stewart and Rachel Hunter, and ex-girlfriend Kelly Emberg.

Penny has previously opened up about the joys of being a stepmother. During a candid chat with HELLO!, she said: "Being a stepmother to start with was very daunting and challenging, but it's proved to be an honour and very rewarding.

Alastair Stewart standing with father Rod Stewart
The rock legend's son is all grown-up (Dave Benett)

"When I first met my husband, his youngest was five and the oldest was 21. So I got to see the different stages that children go through and the challenges they hold, but the rewards as well."

SEE: Penny Lancaster twins with husband Rod Stewart as they board ultra-luxe private jet

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Musing on some of the challenges, Penny went on to add: "It's been a learning curve but a wonderful one. It's so lovely that we're all so close and they all turn to me for advice, to talk about dad, boyfriends and career choices. It’s a big happy family now."