Now Playing: Prince George's first few years

Now Playing: Suspected deadly gas explosion at food shop in China

Now Playing: What ISIS left behind in suburbs of Raqqa, Syria

Now Playing: Prince William, Princess Kate try to make pretzels in Germany

Now Playing: Swimming robot probes Fukushima reactor to find melted fuel

Now Playing: Family holds vigil in Australia for woman fatally shot by Minn. officer

Now Playing: Despite tough talk, Trump admin again certifies Iran's nuclear deal compliance

Now Playing: North Korea 'clearly' has missiles that can reach US, general says

Now Playing: Woman dragged by train on Rome metro

Now Playing: July 21, 2005: Terror attacks on London's public transport system

Now Playing: Battle for Mosul rages on as ISIS loses grip on the city

Now Playing: EU chief to EU parliament leader: 'You are ridiculous'

Now Playing: Cop carries a baby above floodwaters

Now Playing: Huge bonfire explodes in Italy

Now Playing: Heavy rain causes flooding in southwestern Japan; 1 dead

Now Playing: North Korea tests intercontinental ballistic missile

Now Playing: ISIS' 'caliphate' faces collapse, with the future of the territory it claimed in limbo

Now Playing: Mosul's battle zone full of destroyed buildings, roads

Now Playing: North Korea conducts historic test of missile capable of reaching US

Now Playing: President Xi, Chancellor Merkel meet pandas in Berlin