The This Morning star, 39, wished her sister, Kelly Willoughby, a happy 42nd birthday.
Holly shared a video of her smiling with Kelly to her 6.7 Instagram followers.
She captioned the video: "Happy Birthday to my beautiful sister @ladywilloughby LOVE you to pieces... can’t wait to give you a huge squeeze when we can... have the best day... see you on Zoom!"
Kelly is a successful author in her own right.
Despite Kelly sporting much darker hair, the sisters' resemblance remains uncanny.
Many Instagram followers commented on how similar the pair look.
One wrote: "You two look soooo alike" and another posted: "You're so alike x."
A third commented: "Wow two peas, another beautiful lady hope it is the best day."
A fourth wrote: "Wow like twins!!" and a fifth posted: "Both so gorgeous!"
Given Holly's reference to Zoom, the siblings will likely be celebrating Kelly's big day together.
Due to current lockdown rules, social gatherings are not permitted.
Although Kelly keeps a far lower profile than Holly, the pair regularly attend events together.
Kelly has served as Holly's plus one on many occasions, including at the TV Baftas.
She celebrated her 2019 TV Bafta win with Kelly and shared a lovely photo of the pair.
Her caption included: "Just dreamy sharing tonight’s @bafta with my sister."
In an interview with The Guardian in 2014, Holly admitted she and Kelly are like "chalk and cheese".
She said: "We’re more like friends than sisters. We even bought a place together in Putney.
"You would expect some fireworks, but because we have the same friends and have different roles within that group, none of that ever came into it.
"I’m more likely to be the one to say, 'everyone back to mine' and cook for everyone, whereas she’s much better at tidying up."
The pair have maintained social distancing while filming, sitting two metres apart.
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