"Thought it's Martin"- Fans stunned by BTS' Namjoon's blonde transformation in birthday selfie, sparking comparisons to CORTIS' 17-year-old leader

BTS leader Kim Namjoon (RM) turned 31 on September 12, and his birthday instantly became a topic of discussion among fans. While many flooded social media with birthday wishes, it was his surprise transformation that stole the spotlight.

Namjoon posted a mirror selfie on Instagram, where he debuted with striking blonde hair for the first time in years. The story was also accompanied with a short note thanking fans and saying he missed them.

"Thank you. I miss you all," he wrote.

The change sparked chaos online. Many fans did double takes and also joked that they mistook him for Martin. The latter is the 17-year-old leader of HYBE’s rookie boy group CORTIS. An X user, @Sugajoon21, wrote:

"Lol i thought it's martin first i swear to god I'm loyal to bts😭."

Namjoon also shared moments from his intimate celebration, including photos of birthday banners put up by fans, his two-tier cake decorated with a “Let’s stay healthy” message, and a glimpse of his birthday meal.

The resemblance between the two idols with their matching blonde looks set off playful reactions across social platforms. Some fans laughed that Namjoon looked like Martin’s older brother. Others imagined the younger idol beaming after his role model appeared with the same hairstyle.

Alongside the lighthearted jokes, fans praised him for his visuals. They said that he looked like he was debuting all over again.

More on Namjoon’s birthday, Martin comparisons, and BTS’ recent updates

The comparisons to Martin didn’t just stay within fan circles. The BTS rapper himself acknowledged the resemblance during a recent Weverse Live. He mentioned receiving birthday wishes from CORTIS' Martin and TXT’s Taehyun.

He even pointed out that when he met Martin in person, he noticed how similar their hair colors were. According to the translation by user @cortisnewss on X, RM said:

"My hair color? Oh, right. There’s this group called CORTIS who just debuted – Martin, one of the members, sent me a birthday message earlier. When I saw him in person, I realized our hair colors are pretty similar. Martin’s really cool, he’s tall too. He congratulated me."

For fans, the mention was a heartwarming connection between BTS and HYBE’s next-generation boy group.

BTS' RM at Annual United Nations General Assembly (Image via Getty)

Martin has often expressed how much he looks up to RM. In an interview with Spotify, he even credited him as the reason he joined BIGHIT MUSIC. As CORTIS’ leader, Martin said that he draws inspiration from Namjoon’s leadership and artistry.

"The artist I admire is RM from BTS! He's the reason why I came into this company. There's a lot I can learn from him as a leader, I respect him a lot. [RM] if you're watching, we'll try our best to make it big," he said.

In other news, Namjoon has donated 200 million KRW (about $154,000) to two major hospitals in South Korea, namely Seoul Asan Medical Center and Korea University Medical Center. It is to help fund treatments for vulnerable patients. The gesture reinforced his reputation as an artist who balances global stardom with quiet philanthropy.

Other BTS members joined in the celebrations too. Jin gifted Namjoon a luxury diamond ring from French jewelry brand FRED. J-hope posted unseen photos of RM with birthday wishes, while V also shared an Instagram story to mark the day.

With all seven members now reunited after their military service, ARMYs are looking forward to BTS’ spring 2026 comeback album and world tour.

About the author

Mantasha is a pop culture writer at Sportskeeda who covers K-pop and K-drama. She has recently completed her Masters in English and has a rich 3-year writing experience where she crafted engaging content for top companies such as Unacademy, Apollo Hospitals, Adani Airports, and the Economic Times. Her experience has helped her create a strong foundation that complements her passion for creating the best content related to K-pop, K-dramas and Korean movies.

Mantasha's interest in pop culture took root when her cousin introduced her to classic Hollywood and Bollywood tunes and the rest, as they say, is history. Mantasha’s connection with K-pop supergroup BTS is a special one as their song lyrics, hard work, and dedication resonate with her like no other group does.

Maintaining accuracy, relevance, and ethics in her reporting is extremely essential for Mantasha. She prioritizes thorough research, delving deep beyond just superficial sources, to ensure comprehensive and trustworthy information.

When not writing, Mantasha enjoys journaling and doodling, watching K-dramas and listening to songs.

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Edited by Arunava Dutta