Rod Stewart's Wife Welcomed His Kids as Her Own: Now She Celebrates Birthday of Her 'Boy'

• Rod Stewart and his wife celebrate the birthday of their son.

• Despite having only two joint children, Rod Stewart's wife, Penny Lancaster, accepts all his children as her own.

• "Penny has mended my heart in more ways than one," Rod Stewart said about his wife.

November ends on a high note as Rocker Rod Stewart celebrates his son's birthday. The singer and his wife, Penny Lancaster, commemorated their son Alaistair Stewart's 17th birthday with different but equally adorable Instagram posts.

Lancaster celebrated with a post honoring and gushing over how proud she was of her son. In the photo of the mother-son duo, the former model looked gorgeous in a denim jacket, while her son wore a black short-sleeved shirt and a silver chain.

"So proud of my boy. Happy 17th, @alastairwstewart." She captioned the photo. On the other hand, Stewart celebrated his son with a simple photo of the father-son duo captioned:

"Happy Birthday, Lad."

Fans took to the comment section to wish Alaistair a wonderful day and congratulate him on the milestone. Many pointed out how much the 17-year-old looked like a younger version of his dad, while others thought the model, who recently signed a deal with luxury clothing label Palm Angels, looked more like his mom.

Others, however, were surprised at how fast time had flown and could not believe Alastair was already 17. One fan recalls Alaistair being a baby not too many years ago. They wrote:

"Nooo! I can't believe it. I remember being at a Rod concert, and he had just been born."

"Penny Has Mended My Heart": Inside Their 15 Years of Love

Despite the success of his union with Lancaster, Stewart advises young people to forget about marriage until they have lived a little -- advice he wishes he had listened to himself.

Against his father's better judgment, Stewart married young and struggled with settling down into family life because he was not done with partying and drinking. His lifestyle resulted in the death of two of his marriages. Lucky for him, he finally found love with Lancaster after numerous failed relationships and two divorces.

The pair have been married since 2007. When Stewart and Lancaster met in 1999, Stewart was freshly divorced from his second wife, and his bandmate thought he was not ready to test the relationship waters again.

Stewart took her number anyway and gave it to his bandmate, who kept it. Six months later, Stewart asked for the number and asked Penny to dinner, and he could never be more grateful that he did.

Stewart proposed to Lancaster in 2005 atop the Eiffel tower in Paris with a princess-cut diamond ring. They walked down the aisle two years later in Italy, then renewed their vows ten years later at their 45-acre estate in Essex, England.

Stewart says his relationship with Lancaster is perfect; she is his whole world. He says that while love comes in many forms to different people, his version of it is wanting to share everything with Lancaster. He adds:

"[Penny] has mended my heart in more ways than one."

Despite the "Have I Told You Lately That I Love You" singer having six children before they met, Lancaster accepted him and his children. The two even added to the brood and had two more children, sons Alastair and Aiden, now 17 and 12, respectively.

How Is Rod Stewart Coping with His Eight Kids?

Stewart is a father of eight from his various relationships and marriages. And despite a busy working schedule when his kids were growing up, he remained dedicated to them. He is a different father to each of his kids because, as he says:

"You really have to treat all of them as individuals with individual problems."

He had his first baby Sarah with his ex-girlfriend Susannah Boffey; son Sean and daughter Kimberly with his first wife Alana, daughter Ruby with his ex-girlfriend Kelly Emberg; and daughter Renee and son Liam with his second wife, Rachel Hunter.

He says out of all his older kids; only Liam did not have a challenging phase with alcohol and drugs. However, they all managed to get past it. However, that period of his life taught him to listen to his children and, in turn, became a better father.

Today, he says he couldn't ask for anything more than he already has. He loves his children and says his happiest moments are seeing his wife and children smiling.

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