While the pair have often been photographed together, it was believed the pair were just friends, but Holly has claimed they are actually family.
The ‘This Morning’ presenter made the revelation as she posted a picture of her Boxing Day celebrations on Instagram.
She shared a snap of her and Tamzin with another family member, writing: “Me and @glamzin and our Nonna Matriarch! In true #eastendersstyle... faaaaamly! Xxx FYI.., @glamzin is my cousin.”
Tamzin also shared a similar photo, writing: “Boxing Day at the Baldwin’s ... family tradition .... nanny Lina the oldest member at 87 and @hollywilloughby.”
Holly’s Instagram followers couldn’t believe she had been keeping her relation to Tamzing under wraps, with one writing: “How did I not know this?!”, while another said: “Omg did not know this!”
However, there was speculation Tamzin is actually cousins with Holly’s husband, Dan Baldwin, which would make her and Holly cousins-in-law.
A rep for Tamzin confirmed this was the case when contacted by HuffPost UK.
Tamzin is currently gearing up for her on-screen return to ‘EastEnders’ as Mel Owen.
The character will be back in Walford in the New Year after nearly 16 years away, and teasing her comeback in a recent interview with HuffPost UK, Tamzin claimed Mel is back for “a very serious reason”.
“I can tell you she’s back, but she doesn’t want to be back,” Tamzin said. “She’s back for a reason, it’s a very serious reason and she needs to get into that Square and do what she needs to do, and get out again.
“Unfortunately, it takes longer than she expects.”
She continued: “She definitely visits Ian, she definitely visits Phil. She bumps into a few old faces… Sharon. But really the story doesn’t revolve around those people, the reason she’s back doesn’t revolve around them at all.”