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While no relationship between the two has been confirmed, fans of the 55-year-old actor wasted no time in getting rather excited by the prospect of a romance for Reeves. However, while most people were happy to see the pair smiling and holding hands, some were left in a state of shock, having confused Grant, 46, with Dame Helen Mirren.
Taking to social media, many people admitted they thought Reeves may be in a relationship with the 74-year-old Academy Award-winning actor for a moment there.
One person tweeted: "I wasn't wearing my glasses at first and I legit thought he was dating Helen Mirren which I also would have been here for."
Another said: "Did anyone else think when they saw the image of Keanu Reeves with his new partner that she looked like Helen Mirren at first?
"Regardless, I'm very happy for Keanu and hope him and Alexandra have a very loving relationship as they have known each other for a long time."
A third added: "Keanu Reeves is dating a woman my age who kinda looks like Helen Mirren and I have never been more attracted to him."
Mirren has actually been married since 1997, just in case there are any of you out there who still aren't 100 percent sure it wasn't her who walked the red carpet with Reeves.
Grant and Reeves have previously collaborated on the grown-up picture book series Ode To Happiness, first released in 2011, which saw Grant provide the visual art while Reeves wrote the poetry. The business partners also have a publishing house called X Artists' Books.
Reeves' romantic life hasn't been easy. In 1999, he and his girlfriend Jennifer Syme's daughter was stillborn eight months into the pregnancy. A year-and-a-half later, Syme was killed in a car crash.
Since then, Reeves has remained fairly private about his love life, having been linked to the likes of Sandra Bullock and Amanda De Cadenet in the past.
He told Esquire: "I think actors and actresses are maybe a little more private than other celebrities.
"I don't know. I'm a pretty private person. But I don't have anything to tweet, or say, or anything."
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