Meghan Markle's half sister, Samantha, is in the hospital after suffering what appears to be a broken ankle and a fractured knee after a confrontation with the paparazzi ... TMZ has learned.

Samantha's boyfriend, Mark, tells TMZ, they were driving in Florida near a toll booth when they had a "paparazzi confrontation." He says the photog veered in front of them, trying to get a clear shot. Her boyfriend says he swerved to the left in an attempt to avoid him and hit a concrete barrier.

He says Samantha hit the windshield and fell to the floor mat. Samantha, who has MS, was unable to lift herself up.

He says her foot was twisted backward.

He drove Samantha to the E.R. where doctors are treating her.

As we reported, Samantha's father just got out of surgery to repair his heart after a serious heart attack.

He says the paparazzo fled the scene.