Conversation so far:
How many times was Ethel Merman married?
Merman was married and divorced four times.
Who did Ethel Merman marry first?
Her first marriage, in 1940, was to theatrical agent William Smith.
When did Ethel Merman divorce William Smith?
They were divorced in 1941.
When did Ethel Merman after William Smith next marry?
Later that same year, Merman married newspaper executive Robert Levitt.
What happened with Ethel Merman's marriage to Robert Levitt?
Merman and Levitt were divorced in 1952.
When was the next Ethel Merman marriage after Robert Levitt?
In March 1953, Merman married Robert Six, the president of Continental Airlines.

Question: What happened to this marriage?
Self-contained rewrite: What happened to Ethel Merman's marriage to Robert Six?