Glendale, Arizona - Republican presidential candidate Donald Trump is preparing to hold a campaign rally in Arizona, in which an unnamed "secret guest" is promised to make an appearance.

According to the Arizona Republic, the event will take place Friday night at the Desert Diamond Arena in Glendale.

Social media has been buzzing with rumors about whom the Trump campaign's teased guest may be, but many believe it may be Independent presidential candidate Robert F. Kennedy Jr.

On Thursday, Kennedy filed to withdraw his name from the ballot in Arizona, and shortly after noon on Friday, he announced that he was dropping out of the race during a press conference in downtown Phoenix.

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In his speech, he lamented about how he was rejected from the Democratic Party, condemned the selection of Vice President Kamala Harris as the Democratic nominee, and endorsed Trump for president.

Kennedy's exit comes after several reports claimed he had approached both Trump and Harris' campaigns, seeking a job in their presidential administration in exchange for his endorsement.

With Kennedy being in Arizona and recent polls showing Harris closing in on Trump in the state, many believe RFK may be the "special guest."

But when Trump was asked about the endorsement by NBC News early Friday, he responded, "I don't want to get too much into it because you're telling me something I don't know."

The rally is scheduled to begin at 6:00 PM ET and will be streamed on the Trump campaign's Rumble channel.