The phrase "allegedly familiar" is correct and usable in written English.
It can be used when discussing something that is claimed to be known or recognized, but without definitive proof.
Example: "The suspect was allegedly familiar with the crime scene, having visited it several times before."
Alternatives: "reportedly known" or "supposedly recognized".
While less often heard these days, big cheese remains a familiar expression, originating allegedly from a cheese made from all the milk produced in a day by Republicans in the US town of Cheshire for their hero, Thomas Jefferson.
He also lacked access to portions of the Afghan and Iraq databases, said the intelligence official familiar with the case, and allegedly installed unauthorized software on the SIPRnet to get at them.
He asked Udy if she was familiar with the pants Arias was allegedly wearing in the photo.
They decided to pull on a thread that had already been uncovered, according to another person familiar with the investigation — specifically, that Assange allegedly tried to help Manning access the Defense Department computer network by cracking someone else's password.
The file, which was stolen from DNC servers in a hack allegedly connected to Russian intelligence, contained much that will be familiar to those who have closely followed the candidacy of the presumptive Republican nominee.
He allegedly walked up to her and told her she looked familiar before he touched her shoulder and buttocks.
It's become popular among Obama supporters because it shows the allegedly "populist" Hillary's bafflement at operating a device that is familiar to most working Americans.
For anyone not familiar with the story, the Super Bowl star and wide receiver allegedly shot himself in the leg with a concealed handgun at a crowded Manhattan nightclub last Friday night.
U.S. attorneys offices in California and Pennsylvania are investigating the bank's allegedly misleading sales of mortgage-backed securities, according to securities filings and people familiar with the probes.
Asked Friday aboard Air Force One about the Post reporting that Flynn allegedly had not told the truth about the calls, Trump said he was not familiar with it.
