Andi Bauer, 26, and Lara Booth, 23, were hiking through the Romanian mountains when he found himself standing a metre away from a female bear and two cubs.
The protective beast bounded towards PhD student Andi and wrapped its jaws around his right leg - tossing him from side to side.
British Lara - who was walking 20ft behind - screamed for him to "punch it in the eye" and Andi launched his counterattack when the bear tried to strike again.
Miraculously the enormous bear fled, and Lara had to leave Andi to stem the bleeding with his socks while she searched for mobile signal to call for help.
A helicopter took him to hospital where doctors had to screw rods into his leg, which was shattered in three places.
The pair said they feel lucky to be alive.
Andi said: "I was in a state of shock, so I don't remember the pain anymore.
"But this momma bear was suddenly a metre away from me. It was so loud.
"I had my side turned away from it, so when I saw it bounding towards me I just didn't have time to think about what to do.
"It bit my leg, held on to it, and dragged me and threw me about.
"I was crying out for help, but there wasn't anything that anyone could do.
"The bear let go of me, and after Lara told me to punch it in the face, I hit it.
It then went away.
"I suppose I'm lucky I got through it. But I'd have been luckier not being attacked."
Lara from Cambridge added: "I was frozen with fear when we first saw the bears.
"I was probably useless - I was screaming at Andi the whole time.
"Keeping calm during an attack like that is hard. I did so as best I could.
"Then I remembered that you're supposed to punch a bear in the eye, so I yelled that and the bear turned around and left him.
"Andi's so luck to be alive."
Andi, from Germany, and Lara, were hiking through the Carpathian Mountains in southern Romania in May when he was attacked.
The PhD students, living in Berlin, had decided to embark on a five-day expedition from a small town called Breaza after driving from Passau.
They parked their car by an old monastery and priest warned them against climbing the mountains.
Andi and Lara shrugged it off - and scaled the Făgăraș Mountains with just a tent and sleeping bags.
On their first day, Lara and Andi saw a snake, lizard, and six wild boar - and Andi joked: "The next thing we'll see is a bear."
On day two of the trek after walking for around three hours, the pair came across a dead mauled fawn - and started to worry.
Moments later they spotted a bear and two cubs on the path ahead, but it was too late for Andi to safely back away.
Lara started screaming at Andi to get away from the wild animals as they growled with ferociously.
Suddenly, the mother bear bit Andi, grabbed his right ankle, and dragged him away.
Frightened and screaming, Lara tried to keep up with Andi and the bear, all the while keeping her distance from the two cubs.
She didn't have a bear spray with her because Andi had told her she wouldn't need it.
Lara then yelled at Andi that he should punch the bear in the eye - advice she said she'd read online.
After just minutes "that went in slow motion", the bear and her cubs disappeared, leaving Andi wounded on the mountain peak.
It had shattered his bone in three places, and torn a chunk out of his calf, so Andi used his socks as a tourniquet.
After an hour of walking uphill, Lara got phone signal, and called for help, with a helicopter taking her down the mountain before going to get him He was transferred immediately from
Breaza to a hospital in Târgu Mureș, Romania, where he had external fixation to his bone - a cage around his limb.
Lara had to take a series of buses to get to the city hospital 20 miles away, and Andi was later repatriated back to Munich, where he is still in hospital.
She said: "This was supposed to be a hard but pleasant hike through the Romanian mountains.
"I'd read up about bears and panthers, but Andi had persuaded me not to bring a bear spray because he thought it'd be more likely that it would explode.
"I'd had a bad feeling deep down the whole time.
"Leaving him on the mountains on his own was the hardest thing I've ever had to do.
"To keep him safe, I told him to keep speaking loudly to scare other animals off.
"And the whole time I looked for help, another thunderstorm was gathering.
"It was a race against the clock at that point. But we won that one.
"He's doing as best he can now, and is being treated properly in Germany."
Andi added: "I was always feeling optimistic that I would survive the attack.
"In fact, the greater risk was the helicopter not being able to fly through the mountains.
"The chances of being attack by a bear like that are slim anyway - you're more likely for the bear spray to explode than be attacked."