To clarify the title, Clooney didn't propose to Amal from the yet-to-be-opened 1 World Trade Centre observatory, rather CBS invited him there to be the first person to be interviewed from New York's newest landmark building, replacing the Twin Towers.
In the interview, which you can see here in full, he recounts how he "dropped" the proposal on his wife of seven months. Speaking with Charlie Rose, he said: "I knew fairly quickly that I wanted to spend the rest of my life with Amal. When I asked her we had never talked about it. There wasn’t like ‘Maybe we should get married.’ I dropped it on her!"
— House of SJoseph (@JMPasricha) May 20, 2015
So, what did he do? He was at home, he'd done up a playlist of his "Aunt Rosemary's songs. And I asked her and she just kept saying 'WOW'. I said 'I was 53 at the time, or rather 52 at the time (good save), and I said 'I've been on my knee now for about 28 minutes, I gotta get an answer out of this, otherwise I'm gonna throw a hip out. I may not been able to stand back up."
When asked how much his life has changed since getting married, he added: "Well. There are some obvious things. Closet space... And I have someone that I can talk to about anything. Someone who I care more about than I've cared about anyone."
Romantic 'til the last.