Carolyn Kaster, AP
Republican presidential candidate Ben Carson speaks during the Conservative Political Action Conference (CPAC), Friday, March 4, 2016, in National Harbor, Md.

WASHINGTON (AP) — Retired neurosurgeon Ben Carson is expected to endorse his former rival Donald Trump at a news conference Friday morning.

That's according to two people with knowledge of the upcoming endorsement who spoke anonymously because it's not been made public ahead of the formal announcement.

One of the people say Carson was torn between Trump and Texas Sen. Ted Cruz, but opted to support Trump because of a rumor circulated ahead of the Iowa caucuses by the Cruz campaign that Carson had dropped out of the race.

In an interview with Fox News Radio's "John Gibson Show" Thursday, Carson was asked whether he was planning to join the Trump campaign.

"Let's put it this way, I'm certainly leaning," he said, adding that there are "two Donald Trumps" - the one seen on television and the one he's gotten to know behind the scenes.

Trump is expected to formally announce the endorsement at a news conference Friday morning at his Mar-A-Lago Club in West Palm Beach, Florida.